# Buildouts

The word “buildout” refers to a description of a set of parts and the software to create and assemble them. It is often used informally to refer to an installed system based on a buildout definition. For example, if we are creating an application named “Foo”, then “the Foo buildout” is the collection of configuration and application-specific software that allows an instance of the application to be created. We may refer to such an instance of the application informally as “a Foo buildout”.

This document describes how to define buildouts using buildout configuration files and recipes. There are three ways to set up the buildout software and create a buildout instance:

1. Install the zc.buildout egg with easy_install and use the buildout script installed in a Python scripts area.
2. Use the buildout bootstrap script to create a buildout that includes both the setuptools and zc.buildout eggs. This allows you to use the buildout software without modifying a Python install. The buildout script is installed into your buildout local scripts area.
3. Use a buildout command from an already installed buildout to bootstrap a new buildout. (See the section on bootstraping later in this document.)

Often, a software project will be managed in a software repository, such as a subversion repository, that includes some software source directories, buildout configuration files, and a copy of the buildout bootstrap script. To work on the project, one would check out the project from the repository and run the bootstrap script which installs setuptools and zc.buildout into the checkout as well as any parts defined.

We have a sample buildout that we created using the bootstrap command of an existing buildout (method 3 above). It has the absolute minimum information. We have bin, develop-eggs, eggs and parts directories, and a configuration file:

    >>> ls(sample_buildout)
    d  bin
    -  buildout.cfg
    d  develop-eggs
    d  eggs
    d  parts

The bin directory contains scripts.

    >>> ls(sample_buildout, 'bin')
    -  buildout

    >>> ls(sample_buildout, 'eggs')
    -  setuptools-0.7-py3.3.egg
    -  zc.buildout.egg-link

The develop-eggs and parts directories are initially empty:

    >>> ls(sample_buildout, 'develop-eggs')
    >>> ls(sample_buildout, 'parts')

The develop-eggs directory holds egg links for software being developed in the buildout. We separate develop-eggs and other eggs to allow eggs directories to be shared across multiple buildouts. For example, a common developer technique is to define a common eggs directory in their home that all non-develop eggs are stored in. This allows larger buildouts to be set up much more quickly and saves disk space.

The parts directory provides an area where recipes can install part data. For example, if we built a custom Python, we would install it in the part directory. Part data is stored in a sub-directory of the parts directory with the same name as the part.

Buildouts are defined using configuration files. These are in the format defined by the Python ConfigParser module, with extensions that we’ll describe later. By default, when a buildout is run, it looks for the file buildout.cfg in the directory where the buildout is run.

The minimal configuration file has a buildout section that defines no parts:

    >>> cat(sample_buildout, 'buildout.cfg')
    [buildout]
    parts =

A part is simply something to be created by a buildout. It can be almost anything, such as a Python package, a program, a directory, or even a configuration file.

## Recipes

A part is created by a recipe. Recipes are always installed as Python eggs. They can be downloaded from a package server, such as the Python Package Index, or they can be developed as part of a project using a “develop” egg.

A develop egg is a special kind of egg that gets installed as an “egg link” that contains the name of a source directory. Develop eggs don’t have to be packaged for distribution to be used and can be modified in place, which is especially useful while they are being developed.

Let’s create a recipe as part of the sample project. We’ll create a recipe for creating directories. First, we’ll create a recipes source directory for our local recipes:

    >>> mkdir(sample_buildout, 'recipes')

and then we’ll create a source file for our mkdir recipe:

    >>> write(sample_buildout, 'recipes', 'mkdir.py',
    ... """
    ... import logging, os, zc.buildout
    ...
    ... class Mkdir:
    ...
    ...     def __init__(self, buildout, name, options):
    ...         self.name, self.options = name, options
    ...         options['path'] = os.path.join(
    ...                               buildout['buildout']['directory'],
    ...                               options['path'],
    ...                               )
    ...         if not os.path.isdir(os.path.dirname(options['path'])):
    ...             logging.getLogger(self.name).error(
    ...                 'Cannot create %s. %s is not a directory.',
    ...                 options['path'], os.path.dirname(options['path']))
    ...             raise zc.buildout.UserError('Invalid Path')
    ...
    ...
    ...     def install(self):
    ...         path = self.options['path']
    ...         logging.getLogger(self.name).info(
    ...             'Creating directory %s', os.path.basename(path))
    ...         os.mkdir(path)
    ...         return path
    ...
    ...     def update(self):
    ...         pass
    ... """)

Currently, recipes must define 3 methods:

- a constructor,
- an install method, and
- an update method.

The constructor is responsible for updating a parts options to reflect data read from other sections. The buildout system keeps track of whether a part specification has changed. A part specification has changed if it’s options, after adjusting for data read from other sections, has changed, or if the recipe has changed. Only the options for the part are considered. If data are read from other sections, then that information has to be reflected in the parts options. In the Mkdir example, the given path is interpreted relative to the buildout directory, and data from the buildout directory is read. The path option is updated to reflect this. If the directory option was changed in the buildout sections, we would know to update parts created using the mkdir recipe using relative path names.

When buildout is run, it saves configuration data for installed parts in a file named ”.installed.cfg”. In subsequent runs, it compares part-configuration data stored in the .installed.cfg file and the part-configuration data loaded from the configuration files as modified by recipe constructors to decide if the configuration of a part has changed. If the configuration has changed, or if the recipe has changed, then the part is uninstalled and reinstalled. The buildout only looks at the part’s options, so any data used to configure the part needs to be reflected in the part’s options. It is the job of a recipe constructor to make sure that the options include all relevant data.

Of course, parts are also uninstalled if they are no-longer used.

The recipe defines a constructor that takes a buildout object, a part name, and an options dictionary. It saves them in instance attributes. If the path is relative, we’ll interpret it as relative to the buildout directory. The buildout object passed in is a mapping from section name to a mapping of options for that section. The buildout directory is available as the directory option of the buildout section. We normalize the path and save it back into the options directory.

The install method is responsible for creating the part. In this case, we need the path of the directory to create. We’ll use a path option from our options dictionary. The install method logs what it’s doing using the Python logging call. We return the path that we installed. If the part is uninstalled or reinstalled, then the path returned will be removed by the buildout machinery. A recipe install method is expected to return a string, or an iterable of strings containing paths to be removed if a part is uninstalled. For most recipes, this is all of the uninstall support needed. For more complex uninstallation scenarios use Uninstall recipes.

The update method is responsible for updating an already installed part. An empty method is often provided, as in this example, if parts can’t be updated. An update method can return None, a string, or an iterable of strings. If a string or iterable of strings is returned, then the saved list of paths to be uninstalled is updated with the new information by adding any new files returned by the update method.

We need to provide packaging information so that our recipe can be installed as a develop egg. The minimum information we need to specify is a name. For recipes, we also need to define the names of the recipe classes as entry points. Packaging information is provided via a setup.py script:

    >>> write(sample_buildout, 'recipes', 'setup.py',
    ... """
    ... from setuptools import setup
    ...
    ... setup(
    ...     name = "recipes",
    ...     entry_points = {'zc.buildout': ['mkdir = mkdir:Mkdir']},
    ...     )
    ... """)

Our setup script defines an entry point. Entry points provide a way for an egg to define the services it provides. Here we’ve said that we define a zc.buildout entry point named mkdir. Recipe classes must be exposed as entry points in the zc.buildout group. we give entry points names within the group.

We also need a README.txt for our recipes to avoid an annoying warning from distutils, on which setuptools and zc.buildout are based:

    >>> write(sample_buildout, 'recipes', 'README.txt', " ")

Now let’s update our buildout.cfg:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = data-dir
    ...
    ... [data-dir]
    ... recipe = recipes:mkdir
    ... path = mystuff
    ... """)

Let’s go through the changes one by one:

    develop = recipes

This tells the buildout to install a development egg for our recipes. Any number of paths can be listed. The paths can be relative or absolute. If relative, they are treated as relative to the buildout directory. They can be directory or file paths. If a file path is given, it should point to a Python setup script. If a directory path is given, it should point to a directory containing a setup.py file. Development eggs are installed before building any parts, as they may provide locally-defined recipes needed by the parts.

    parts = data-dir

Here we’ve named a part to be “built”. We can use any name we want except that different part names must be unique and recipes will often use the part name to decide what to do.

    [data-dir]
    recipe = recipes:mkdir
    path = mystuff

When we name a part, we also create a section of the same name that contains part data. In this section, we’ll define the recipe to be used to install the part. In this case, we also specify the path to be created.

Let’s run the buildout. We do so by running the build script in the buildout:

    >>> import os
    >>> os.chdir(sample_buildout)
    >>> buildout = os.path.join(sample_buildout, 'bin', 'buildout')
    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Installing data-dir.
    data-dir: Creating directory mystuff

We see that the recipe created the directory, as expected:

    >>> ls(sample_buildout)
    -  .installed.cfg
    d  bin
    -  buildout.cfg
    d  develop-eggs
    d  eggs
    d  mystuff
    d  parts
    d  recipes

In addition, .installed.cfg has been created containing information about the part we installed:

    >>> cat(sample_buildout, '.installed.cfg')
    [buildout]
    installed_develop_eggs = /sample-buildout/develop-eggs/recipes.egg-link
    parts = data-dir

    [data-dir]
    __buildout_installed__ = /sample-buildout/mystuff
    __buildout_signature__ = recipes-c7vHV6ekIDUPy/7fjAaYjg==
    path = /sample-buildout/mystuff
    recipe = recipes:mkdir

Note that the directory we installed is included in .installed.cfg. In addition, the path option includes the actual destination directory.

If we change the name of the directory in the configuration file, we’ll see that the directory gets removed and recreated:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = data-dir
    ...
    ... [data-dir]
    ... recipe = recipes:mkdir
    ... path = mydata
    ... """)

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling data-dir.
    Installing data-dir.
    data-dir: Creating directory mydata

    >>> ls(sample_buildout)
    -  .installed.cfg
    d  bin
    -  buildout.cfg
    d  develop-eggs
    d  eggs
    d  mydata
    d  parts
    d  recipes

If any of the files or directories created by a recipe are removed, the part will be reinstalled:

    >>> rmdir(sample_buildout, 'mydata')
    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling data-dir.
    Installing data-dir.
    data-dir: Creating directory mydata

## Error reporting

If a user makes an error, an error needs to be printed and work needs to stop. This is accomplished by logging a detailed error message and then raising a (or an instance of a subclass of a) zc.buildout.UserError exception. Raising an error other than a UserError still displays the error, but labels it as a bug in the buildout software or recipe. In the sample above, of someone gives a non-existent directory to create the directory in:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = data-dir
    ...
    ... [data-dir]
    ... recipe = recipes:mkdir
    ... path = /xxx/mydata
    ... """)

We’ll get a user error, not a traceback.

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    data-dir: Cannot create /xxx/mydata. /xxx is not a directory.
    While:
      Installing.
      Getting section data-dir.
      Initializing section data-dir.
    Error: Invalid Path

## Recipe Error Handling

If an error occurs during installation, it is up to the recipe to clean up any system side effects, such as files created. Let’s update the mkdir recipe to support multiple paths:

    >>> write(sample_buildout, 'recipes', 'mkdir.py',
    ... """
    ... import logging, os, zc.buildout
    ...
    ... class Mkdir:
    ...
    ...     def __init__(self, buildout, name, options):
    ...         self.name, self.options = name, options
    ...
    ...         # Normalize paths and check that their parent
    ...         # directories exist:
    ...         paths = []
    ...         for path in options['path'].split():
    ...             path = os.path.join(buildout['buildout']['directory'], path)
    ...             if not os.path.isdir(os.path.dirname(path)):
    ...                 logging.getLogger(self.name).error(
    ...                     'Cannot create %s. %s is not a directory.',
    ...                     options['path'], os.path.dirname(options['path']))
    ...                 raise zc.buildout.UserError('Invalid Path')
    ...             paths.append(path)
    ...         options['path'] = ' '.join(paths)
    ...
    ...     def install(self):
    ...         paths = self.options['path'].split()
    ...         for path in paths:
    ...             logging.getLogger(self.name).info(
    ...                 'Creating directory %s', os.path.basename(path))
    ...             os.mkdir(path)
    ...         return paths
    ...
    ...     def update(self):
    ...         pass
    ... """)

    >>> clean_up_pyc(sample_buildout, 'recipes', 'mkdir.py')

If there is an error creating a path, the install method will exit and leave previously created paths in place:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = data-dir
    ...
    ... [data-dir]
    ... recipe = recipes:mkdir
    ... path = foo bin
    ... """)

    >>> print_(system(buildout))
    Develop: '/sample-buildout/recipes'
    Uninstalling data-dir.
    Installing data-dir.
    data-dir: Creating directory foo
    data-dir: Creating directory bin
    While:
      Installing data-dir.

    An internal error occurred due to a bug in either zc.buildout or in a
    recipe being used:
    ... exists...

We meant to create a directory bins, but typed bin. Now foo was left behind.

    >>> os.path.exists('foo')
    True

If we fix the typo:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = data-dir
    ...
    ... [data-dir]
    ... recipe = recipes:mkdir
    ... path = foo bins
    ... """)

    >>> print_(system(buildout))
    Develop: '/sample-buildout/recipes'
    Installing data-dir.
    data-dir: Creating directory foo
    While:
      Installing data-dir.

    An internal error occurred due to a bug in either zc.buildout or in a
    recipe being used:
    ... exists...

Now they fail because foo exists, because it was left behind.

    >>> remove('foo')

Let’s fix the recipe:

    >>> write(sample_buildout, 'recipes', 'mkdir.py',
    ... """
    ... import logging, os, zc.buildout, sys
    ...
    ... class Mkdir:
    ...
    ...     def __init__(self, buildout, name, options):
    ...         self.name, self.options = name, options
    ...
    ...         # Normalize paths and check that their parent
    ...         # directories exist:
    ...         paths = []
    ...         for path in options['path'].split():
    ...             path = os.path.join(buildout['buildout']['directory'], path)
    ...             if not os.path.isdir(os.path.dirname(path)):
    ...                 logging.getLogger(self.name).error(
    ...                     'Cannot create %s. %s is not a directory.',
    ...                     options['path'], os.path.dirname(options['path']))
    ...                 raise zc.buildout.UserError('Invalid Path')
    ...             paths.append(path)
    ...         options['path'] = ' '.join(paths)
    ...
    ...     def install(self):
    ...         paths = self.options['path'].split()
    ...         created = []
    ...         try:
    ...             for path in paths:
    ...                 logging.getLogger(self.name).info(
    ...                     'Creating directory %s', os.path.basename(path))
    ...                 os.mkdir(path)
    ...                 created.append(path)
    ...         except Exception:
    ...             for d in created:
    ...                 os.rmdir(d)
    ...                 assert not os.path.exists(d)
    ...                 logging.getLogger(self.name).info(
    ...                     'Removed %s due to error',
    ...                      os.path.basename(d))
    ...             sys.stderr.flush()
    ...             sys.stdout.flush()
    ...             raise
    ...
    ...         return paths
    ...
    ...     def update(self):
    ...         pass
    ... """)

    >>> clean_up_pyc(sample_buildout, 'recipes', 'mkdir.py')

And put back the typo:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = data-dir
    ...
    ... [data-dir]
    ... recipe = recipes:mkdir
    ... path = foo bin
    ... """)

When we rerun the buildout:

    >>> print_(system(buildout))
    Develop: '/sample-buildout/recipes'
    Installing data-dir.
    data-dir: Creating directory foo
    data-dir: Creating directory bin
    data-dir: Removed foo due to error
    While:
      Installing data-dir.

    An internal error occurred due to a bug in either zc.buildout or in a
    recipe being used:
    ... exists...

we get the same error, but we don’t get the directory left behind:

    >>> os.path.exists('foo')
    False

It’s critical that recipes clean up partial effects when errors occur. Because recipes most commonly create files and directories, buildout provides a helper API for removing created files when an error occurs. Option objects have a created method that can be called to record files as they are created. If the install or update method returns with an error, then any registered paths are removed automatically. The method returns the files registered and can be used to return the files created. Let’s use this API to simplify the recipe:

    >>> write(sample_buildout, 'recipes', 'mkdir.py',
    ... """
    ... import logging, os, zc.buildout
    ...
    ... class Mkdir:
    ...
    ...     def __init__(self, buildout, name, options):
    ...         self.name, self.options = name, options
    ...
    ...         # Normalize paths and check that their parent
    ...         # directories exist:
    ...         paths = []
    ...         for path in options['path'].split():
    ...             path = os.path.join(buildout['buildout']['directory'], path)
    ...             if not os.path.isdir(os.path.dirname(path)):
    ...                 logging.getLogger(self.name).error(
    ...                     'Cannot create %s. %s is not a directory.',
    ...                     options['path'], os.path.dirname(options['path']))
    ...                 raise zc.buildout.UserError('Invalid Path')
    ...             paths.append(path)
    ...         options['path'] = ' '.join(paths)
    ...
    ...     def install(self):
    ...         paths = self.options['path'].split()
    ...         for path in paths:
    ...             logging.getLogger(self.name).info(
    ...                 'Creating directory %s', os.path.basename(path))
    ...             os.mkdir(path)
    ...             self.options.created(path)
    ...
    ...         return self.options.created()
    ...
    ...     def update(self):
    ...         pass
    ... """)

    >>> clean_up_pyc(sample_buildout, 'recipes', 'mkdir.py')

We returned by calling created, taking advantage of the fact that it returns the registered paths. We did this for illustrative purposes. It would be simpler just to return the paths as before.

If we rerun the buildout, again, we’ll get the error and no directories will be created:

    >>> print_(system(buildout))
    Develop: '/sample-buildout/recipes'
    Installing data-dir.
    data-dir: Creating directory foo
    data-dir: Creating directory bin
    While:
      Installing data-dir.

    An internal error occurred due to a bug in either zc.buildout or in a
    recipe being used:
    ... exists...

    >>> os.path.exists('foo')
    False

Now, we’ll fix the typo again and we’ll get the directories we expect:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = data-dir
    ...
    ... [data-dir]
    ... recipe = recipes:mkdir
    ... path = foo bins
    ... """)

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Installing data-dir.
    data-dir: Creating directory foo
    data-dir: Creating directory bins

    >>> os.path.exists('foo')
    True
    >>> os.path.exists('bins')
    True

## Configuration file syntax

A buildout configuration file consists of a sequence of sections. A section has a section header followed by 0 or more section options. (Buildout configuration files may be viewed as a variation on INI files.)

A section header consists of a section name enclosed in square braces. A section name consists of one or more non-whitespace characters other than square braces (‘[‘, ‘]’), curly braces (‘{‘, ‘}’), colons (‘:’) or equal signs (‘=’). Whitespace surrounding section names is ignored.

A section header can optionally have a condition expression separated by a colon. See Conditional sections.

Options consist of option names, followed by optional space or tab characters, an optional plus or minus sign and an equal signs and values. An option value may be spread over multiple lines as long as the lines after the first start with a whitespace character. An option name consists of one or more non-whitespace characters other than equal signs, square braces (“[”, “]”), curly braces (“{”, “}”), plus signs or colons (”:”). The option name ‘<’ is reserved. An option’s data consists of the characters following the equal sign on the start line, plus the continuation lines.

Option values have extra whitespace stripped. How this is done depends on whether the value has non-whitespace characterts on the first line. If an option value has non-whitespace characters on the first line, then each line is stripped and blank lines are removed. For example, in:

    [foo]
    bar = 1
    baz = a
          b

          c

The value of of `bar` is `'1'` and the value of `baz` is `'a\nb\nc'`.

If the first line of an option doesn’t contain whitespace, then the value is dedented (with `textwrap.dedent`), trailing spaces in lines are removed, and leading and trailing blank lines are removed. For example, in:

    [foo]
    bar =
    baz =

      a
        b

      c

The value of bar is `''`, and the value of baz is `'a\n b\n\nc'`.

Lines starting with ‘#’ or ‘;’ characters are comments. Comments can also be placed after the closing square bracket (‘]’) in a section header.

Buildout configuration data are Python strings, which are bytes in Python 2 and unicode in Python 3.

Sections and options within sections may be repeated. Multiple occurrences of of a section are treated as if they were concatenated. The last option value for a given name in a section overrides previous values.

In addition top the syntactic details above:

- option names are case sensitive
- option values can use a substitution syntax, described below, to refer to option values in specific sections.
- option values can be appended or removed using the - and + operators.

## Annotated sections

When used with the annotate command, buildout displays annotated sections. All sections are displayed, sorted alphabetically. For each section, all key-value pairs are displayed, sorted alphabetically, along with the origin of the value (file name or COMPUTED_VALUE, DEFAULT_VALUE, COMMAND_LINE_VALUE).

    >>> print_(system(buildout+ ' annotate'), end='')
    ...

    Annotated sections
    ==================

    [buildout]
    allow-hosts= *
        DEFAULT_VALUE
    allow-picked-versions= true
        DEFAULT_VALUE
    bin-directory= bin
        DEFAULT_VALUE
    develop= recipes
        /sample-buildout/buildout.cfg
    develop-eggs-directory= develop-eggs
        DEFAULT_VALUE
    directory= /sample-buildout
        COMPUTED_VALUE
    eggs-directory= eggs
        DEFAULT_VALUE
    executable= ...
        DEFAULT_VALUE
    find-links=
        DEFAULT_VALUE
    install-from-cache= false
        DEFAULT_VALUE
    installed= .installed.cfg
        DEFAULT_VALUE
    log-format=
        DEFAULT_VALUE
    log-level= INFO
        DEFAULT_VALUE
    newest= true
        DEFAULT_VALUE
    offline= false
        DEFAULT_VALUE
    parts= data-dir
        /sample-buildout/buildout.cfg
    parts-directory= parts
        DEFAULT_VALUE
    prefer-final= true
        DEFAULT_VALUE
    python= buildout
        DEFAULT_VALUE
    show-picked-versions= false
        DEFAULT_VALUE
    socket-timeout=
        DEFAULT_VALUE
    update-versions-file=
        DEFAULT_VALUE
    use-dependency-links= true
        DEFAULT_VALUE
    versions= versions
        DEFAULT_VALUE

    [data-dir]
    path= foo bins
        /sample-buildout/buildout.cfg
    recipe= recipes:mkdir
        /sample-buildout/buildout.cfg

    [versions]
    zc.buildout= >=1.99
        DEFAULT_VALUE
    zc.recipe.egg= >=1.99
        DEFAULT_VALUE

## Variable substitutions

Buildout configuration files support variable substitution. To illustrate this, we’ll create an debug recipe to allow us to see interactions with the buildout:

    >>> write(sample_buildout, 'recipes', 'debug.py',
    ... """
    ... import sys
    ... class Debug:
    ...
    ...     def __init__(self, buildout, name, options):
    ...         self.buildout = buildout
    ...         self.name = name
    ...         self.options = options
    ...
    ...     def install(self):
    ...         for option, value in sorted(self.options.items()):
    ...             sys.stdout.write('%s %s\\n' % (option, value))
    ...         return ()
    ...
    ...     update = install
    ... """)

This recipe doesn’t actually create anything. The install method doesn’t return anything, because it didn’t create any files or directories.

We also have to update our setup script:

    >>> write(sample_buildout, 'recipes', 'setup.py',
    ... """
    ... from setuptools import setup
    ... entry_points = (
    ... '''
    ... [zc.buildout]
    ... mkdir = mkdir:Mkdir
    ... debug = debug:Debug
    ... ''')
    ... setup(name="recipes", entry_points=entry_points)
    ... """)

We’ve rearranged the script a bit to make the entry points easier to edit. In particular, entry points are now defined as a configuration string, rather than a dictionary.

Let’s update our configuration to provide variable substitution examples:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = data-dir debug
    ... log-level = INFO
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... File-1 = ${data-dir:path}/file
    ... File-2 = ${debug:File-1}/log
    ...
    ... [data-dir]
    ... recipe = recipes:mkdir
    ... path = mydata
    ... """)

We used a string-template substitution for File-1 and File-2. This type of substitution uses the string.Template syntax. Names substituted are qualified option names, consisting of a section name and option name joined by a colon.

Now, if we run the buildout, we’ll see the options with the values substituted.

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling data-dir.
    Installing data-dir.
    data-dir: Creating directory mydata
    Installing debug.
    File-1 /sample-buildout/mydata/file
    File-2 /sample-buildout/mydata/file/log
    recipe recipes:debug

Note that the substitution of the data-dir path option reflects the update to the option performed by the mkdir recipe.

It might seem surprising that mydata was created again. This is because we changed our recipes package by adding the debug module. The buildout system didn’t know if this module could effect the mkdir recipe, so it assumed it could and reinstalled mydata. If we rerun the buildout:

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Updating data-dir.
    Updating debug.
    File-1 /sample-buildout/mydata/file
    File-2 /sample-buildout/mydata/file/log
    recipe recipes:debug

We can see that mydata was not recreated.

Note that, in this case, we didn’t specify a log level, so we didn’t get output about what the buildout was doing.

Section and option names in variable substitutions are only allowed to contain alphanumeric characters, hyphens, periods and spaces. This restriction might be relaxed in future releases.

We can omit the section name in a variable substitution to refer to the current section. We can also use the special option, _buildout_section_name_ to get the current section name.

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = data-dir debug
    ... log-level = INFO
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... File-1 = ${data-dir:path}/file
    ... File-2 = ${:File-1}/log
    ... my_name = ${:_buildout_section_name_}
    ...
    ... [data-dir]
    ... recipe = recipes:mkdir
    ... path = mydata
    ... """)

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Updating data-dir.
    Installing debug.
    File-1 /sample-buildout/mydata/file
    File-2 /sample-buildout/mydata/file/log
    my_name debug
    recipe recipes:debug

## Automatic part selection and ordering

When a section with a recipe is referred to, either through variable substitution or by an initializing recipe, the section is treated as a part and added to the part list before the referencing part. For example, we can leave data-dir out of the parts list:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug
    ... log-level = INFO
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... File-1 = ${data-dir:path}/file
    ... File-2 = ${debug:File-1}/log
    ...
    ... [data-dir]
    ... recipe = recipes:mkdir
    ... path = mydata
    ... """)

It will still be treated as a part:

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Updating data-dir.
    Installing debug.
    File-1 /sample-buildout/mydata/file
    File-2 /sample-buildout/mydata/file/log
    recipe recipes:debug

    >>> cat('.installed.cfg')
    [buildout]
    installed_develop_eggs = /sample-buildout/develop-eggs/recipes.egg-link
    parts = data-dir debug
    ...

Note that the data-dir part is included before the debug part, because the debug part refers to the data-dir part. Even if we list the data-dir part after the debug part, it will be included before:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug data-dir
    ... log-level = INFO
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... File-1 = ${data-dir:path}/file
    ... File-2 = ${debug:File-1}/log
    ...
    ... [data-dir]
    ... recipe = recipes:mkdir
    ... path = mydata
    ... """)

It will still be treated as a part:

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Updating data-dir.
    Updating debug.
    File-1 /sample-buildout/mydata/file
    File-2 /sample-buildout/mydata/file/log
    recipe recipes:debug

    >>> cat('.installed.cfg')
    [buildout]
    installed_develop_eggs = /sample-buildout/develop-eggs/recipes.egg-link
    parts = data-dir debug
    ...

## Extending sections (macros)

A section (other than the buildout section) can extend one or more other sections using the `<` option. Options from the referenced sections are copied to the referring section before variable substitution. This, together with the ability to refer to variables of the current section allows sections to be used as macros.

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = myfiles
    ... log-level = INFO
    ...
    ... [debug]
    ... recipe = recipes:debug
    ...
    ... [with_file1]
    ... <= debug
    ... file1 = ${:path}/file1
    ... color = red
    ...
    ... [with_file2]
    ... <= debug
    ... file2 = ${:path}/file2
    ... color = blue
    ...
    ... [myfiles]
    ... <= with_file1
    ...    with_file2
    ... path = mydata
    ... """)

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Uninstalling data-dir.
    Installing myfiles.
    color blue
    file1 mydata/file1
    file2 mydata/file2
    path mydata
    recipe recipes:debug

In this example, the debug, with_file1 and with_file2 sections act as macros. In particular, the variable substitutions are performed relative to the myfiles section.

## Conditional sections

Sometimes, you need different configuration in different environments (different operating systems, or different versions of Python). To make this easier, you can define environment-specific options by providing conditional sections:

    [ctl]
    suffix =

    [ctl:windows]
    suffix = .bat

In this tiny example, we’ve defined a `ctl:suffix` option that’s `.bat` on Windows and an empty string elsewhere.

A conditional section has a colon and then a Python expression after the name. If the Python expression result is true, the section options from the section are included. If the value is false, the section is ignored.

Some things to note:

- If there is no exception, then options from the section are included.
- Sections and options can be repeated. If an option is repeated, the last value is used. In the example above, on Windows, the second `suffix` option overrides the first. If the order of the sections was reversed, the conditional section would have no effect.

In addition to the normal built-ins, the expression has access to global variable that make common cases short and description as shown above:

sys
  the `sys` module
os
  the `os` module
platform
  the `platform` module
re
  The `re` module
python2
  We’re running Python 2
python3
  We’re running Python 3
python26
  We’re running Python 2.6
python27
  We’re running Python 2.7
python32
  We’re running Python 3.2
python33
  We’re running Python 3.3
sys_version
  `sys.version.lower()`
pypy
  We’re running PyPy
jython
  We’re running Jython
iron
  We’re running Iron Python
cpython
  We’re not running PyPy, Jython, or Iron Python
sys_platform
  `str(sys.platform).lower()`
linux
  We’re running on linux
windows
  We’re running on Windows
cygwin
  We’re running on cygwin
solaris
  We’re running on solaris
macosx
  We’re running on Mac OS X
posix
  We’re running on a POSIX-compatible system
bits32
  We’re running on a 32-bit system.
bits64
  We’re running on a 64-bit system.
little_endian
  We’re running on a little-endian system
big_endian
  We’re running on a little-endian system

Expressions must not contain either the `#` or the `;` character.

## Adding and removing options

We can append and remove values to an option by using the + and - operators.

This is illustrated below; first we define a base configuration.

    >>> write(sample_buildout, 'base.cfg',
    ... """
    ... [buildout]
    ... parts = part1 part2 part3
    ...
    ... [part1]
    ... recipe =
    ... option = a1 a2
    ...
    ... [part2]
    ... recipe =
    ... option = b1 b2 b3 b4
    ...
    ... [part3]
    ... recipe =
    ... option = c1 c2
    ...
    ... [part4]
    ... recipe =
    ... option = d2
    ...     d3
    ...     d5
    ...
    ... """)

Extending this configuration, we can “adjust” the values set in the base configuration file.

    >>> write(sample_buildout, 'extension1.cfg',
    ... """
    ... [buildout]
    ... extends = base.cfg
    ...
    ... # appending values
    ... [part1]
    ... option += a3 a4
    ...
    ... # removing values
    ... [part2]
    ... option -= b1 b2
    ...
    ... # alt. spelling
    ... [part3]
    ... option+=c3 c4 c5
    ...
    ... # combining both adding and removing
    ... [part4]
    ... option += d1
    ...      d4
    ... option -= d5
    ...
    ... # normal assignment
    ... [part5]
    ... option = h1 h2
    ...
    ... """)

An additional extension.

    >>> write(sample_buildout, 'extension2.cfg',
    ... """
    ... [buildout]
    ... extends = extension1.cfg
    ...
    ... # appending values
    ... [part1]
    ... option += a5
    ...
    ... # removing values
    ... [part2]
    ... option -= b1 b2 b3
    ...
    ... """)

To verify that the options are adjusted correctly, we’ll set up an extension that prints out the options.

    >>> mkdir(sample_buildout, 'demo')
    >>> write(sample_buildout, 'demo', 'demo.py',
    ... """
    ... import sys
    ... def ext(buildout):
    ...     sys.stdout.write(str(
    ...         [part['option'] for name, part in sorted(buildout.items())
    ...          if name.startswith('part')])+'\\n')
    ... """)

    >>> write(sample_buildout, 'demo', 'setup.py',
    ... """
    ... from setuptools import setup
    ...
    ... setup(
    ...     name="demo",
    ...     entry_points={'zc.buildout.extension': ['ext = demo:ext']},
    ...     )
    ... """)

Set up a buildout configuration for this extension.

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = demo
    ... parts =
    ... """)

    >>> os.chdir(sample_buildout)
    >>> print_(system(os.path.join(sample_buildout, 'bin', 'buildout')), end='')
    ...
    Develop: '/sample-buildout/demo'...

Verify option values.

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = demo
    ... extensions = demo
    ... extends = extension2.cfg
    ... """)

    >>> print_(system(os.path.join('bin', 'buildout')), end='')
    ['a1 a2/na3 a4/na5', 'b1 b2 b3 b4', 'c1 c2/nc3 c4 c5', 'd2/nd3/nd1/nd4', 'h1 h2']
    Develop: '/sample-buildout/demo'

Annotated sections output shows which files are responsible for which operations.

    >>> print_(system(os.path.join('bin', 'buildout') + ' annotate'), end='')
    ...

    Annotated sections
    ==================
    ...

    [part1]
    option= a1 a2
    a3 a4
    a5
        /sample-buildout/base.cfg
    +=  /sample-buildout/extension1.cfg
    +=  /sample-buildout/extension2.cfg
    recipe=
        /sample-buildout/base.cfg

    [part2]
    option= b1 b2 b3 b4
        /sample-buildout/base.cfg
    -=  /sample-buildout/extension1.cfg
    -=  /sample-buildout/extension2.cfg
    recipe=
        /sample-buildout/base.cfg

    [part3]
    option= c1 c2
    c3 c4 c5
        /sample-buildout/base.cfg
    +=  /sample-buildout/extension1.cfg
    recipe=
        /sample-buildout/base.cfg

    [part4]
    option= d2
    d3
    d1
    d4
        /sample-buildout/base.cfg
    +=  /sample-buildout/extension1.cfg
    -=  /sample-buildout/extension1.cfg
    recipe=
        /sample-buildout/base.cfg

    [part5]
    option= h1 h2
        /sample-buildout/extension1.cfg
    [versions]
    zc.buildout= >=1.99
        DEFAULT_VALUE
    zc.recipe.egg= >=1.99
        DEFAULT_VALUE

Cleanup.

    >>> os.remove(os.path.join(sample_buildout, 'base.cfg'))
    >>> os.remove(os.path.join(sample_buildout, 'extension1.cfg'))
    >>> os.remove(os.path.join(sample_buildout, 'extension2.cfg'))

## Multiple configuration files

A configuration file can “extend” another configuration file. Options are read from the other configuration file if they aren’t already defined by your configuration file.

The configuration files your file extends can extend other configuration files. The same file may be used more than once although, of course, cycles aren’t allowed.

To see how this works, we use an example:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... extends = base.cfg
    ...
    ... [debug]
    ... op = buildout
    ... """)

    >>> write(sample_buildout, 'base.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... op = base
    ... """)

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Installing debug.
    op buildout
    recipe recipes:debug

The example is pretty trivial, but the pattern it illustrates is pretty common. In a more practical example, the base buildout might represent a product and the extending buildout might be a customization.

Here is a more elaborate example.

    >>> other = tmpdir('other')

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... extends = b1.cfg b2.cfg %(b3)s
    ...
    ... [debug]
    ... op = buildout
    ... """ % dict(b3=os.path.join(other, 'b3.cfg')))

    >>> write(sample_buildout, 'b1.cfg',
    ... """
    ... [buildout]
    ... extends = base.cfg
    ...
    ... [debug]
    ... op1 = b1 1
    ... op2 = b1 2
    ... """)

    >>> write(sample_buildout, 'b2.cfg',
    ... """
    ... [buildout]
    ... extends = base.cfg
    ...
    ... [debug]
    ... op2 = b2 2
    ... op3 = b2 3
    ... """)

    >>> write(other, 'b3.cfg',
    ... """
    ... [buildout]
    ... extends = b3base.cfg
    ...
    ... [debug]
    ... op4 = b3 4
    ... """)

    >>> write(other, 'b3base.cfg',
    ... """
    ... [debug]
    ... op5 = b3base 5
    ... """)

    >>> write(sample_buildout, 'base.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... name = base
    ... """)

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Installing debug.
    name base
    op buildout
    op1 b1 1
    op2 b2 2
    op3 b2 3
    op4 b3 4
    op5 b3base 5
    recipe recipes:debug

There are several things to note about this example:

- We can name multiple files in an extends option.
- We can reference files recursively.
- Relative file names in extended options are interpreted relative to the directory containing the referencing configuration file.

## Loading Configuration from URLs

Configuration files can be loaded from URLs. To see how this works, we’ll set up a web server with some configuration files.

    >>> server_data = tmpdir('server_data')

    >>> write(server_data, "r1.cfg",
    ... """
    ... [debug]
    ... op1 = r1 1
    ... op2 = r1 2
    ... """)

    >>> write(server_data, "r2.cfg",
    ... """
    ... [buildout]
    ... extends = r1.cfg
    ...
    ... [debug]
    ... op2 = r2 2
    ... op3 = r2 3
    ... """)

    >>> server_url = start_server(server_data)

    >>> write('client.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug
    ... extends = %(url)s/r2.cfg
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... name = base
    ... """ % dict(url=server_url))

    >>> print_(system(buildout+ ' -c client.cfg'), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Installing debug.
    name base
    op1 r1 1
    op2 r2 2
    op3 r2 3
    recipe recipes:debug

Here we specified a URL for the file we extended. The file we downloaded, itself referred to a file on the server using a relative URL reference. Relative references are interpreted relative to the base URL when they appear in configuration files loaded via URL.

We can also specify a URL as the configuration file to be used by a buildout.

    >>> os.remove('client.cfg')
    >>> write(server_data, 'remote.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug
    ... extends = r2.cfg
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... name = remote
    ... """)

    >>> print_(system(buildout + ' -c ' + server_url + '/remote.cfg'), end='')
    While:
      Initializing.
    Error: Missing option: buildout:directory

Normally, the buildout directory defaults to directory containing a configuration file. This won’t work for configuration files loaded from URLs. In this case, the buildout directory would normally be defined on the command line:

    >>> print_(system(buildout
    ...              + ' -c ' + server_url + '/remote.cfg'
    ...              + ' buildout:directory=' + sample_buildout
    ...              ), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Installing debug.
    name remote
    op1 r1 1
    op2 r2 2
    op3 r2 3
    recipe recipes:debug

## User defaults

If the file $HOME/.buildout/default.cfg, exists, it is read before reading the configuration file. ($HOME is the value of the HOME environment variable. The ‘/’ is replaced by the operating system file delimiter.)

    >>> old_home = os.environ['HOME']
    >>> home = tmpdir('home')
    >>> mkdir(home, '.buildout')
    >>> write(home, '.buildout', 'default.cfg',
    ... """
    ... [debug]
    ... op1 = 1
    ... op7 = 7
    ... """)

    >>> os.environ['HOME'] = home
    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Installing debug.
    name base
    op buildout
    op1 b1 1
    op2 b2 2
    op3 b2 3
    op4 b3 4
    op5 b3base 5
    op7 7
    recipe recipes:debug

A buildout command-line argument, -U, can be used to suppress reading user defaults:

    >>> print_(system(buildout + ' -U'), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Installing debug.
    name base
    op buildout
    op1 b1 1
    op2 b2 2
    op3 b2 3
    op4 b3 4
    op5 b3base 5
    recipe recipes:debug

    >>> os.environ['HOME'] = old_home

## Log level

We can control the level of logging by specifying a log level in out configuration file. For example, so suppress info messages, we can set the logging level to WARNING

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... log-level = WARNING
    ... extends = b1.cfg b2.cfg
    ... """)

    >>> print_(system(buildout), end='')
    name base
    op1 b1 1
    op2 b2 2
    op3 b2 3
    recipe recipes:debug

## Socket timeout

The timeout of the connections to egg and configuration servers can be configured in the buildout section. Its value is configured in seconds.

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... socket-timeout = 5
    ... develop = recipes
    ... parts = debug
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... op = timeout
    ... """)

    >>> print_(system(buildout), end='')
    Setting socket time out to 5 seconds.
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Installing debug.
    op timeout
    recipe recipes:debug

If the socket-timeout is not numeric, a warning is issued and the default timeout of the Python socket module is used.

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... socket-timeout = 5s
    ... develop = recipes
    ... parts = debug
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... op = timeout
    ... """)

    >>> print_(system(buildout), end='')
    Default socket timeout is used !
    Value in configuration is not numeric: [5s].

    Develop: '/sample-buildout/recipes'
    Updating debug.
    op timeout
    recipe recipes:debug

## Uninstall recipes

As we’ve seen, when parts are installed, buildout keeps track of files and directories that they create. When the parts are uninstalled these files and directories are deleted.

Sometimes more clean up is needed. For example, a recipe might add a system service by calling chkconfig –add during installation. Later during uninstallation, chkconfig –del will need to be called to remove the system service.

In order to deal with these uninstallation issues, you can register uninstall recipes. Uninstall recipes are registered using the ‘zc.buildout.uninstall’ entry point. Parts specify uninstall recipes using the ‘uninstall’ option.

In comparison to regular recipes, uninstall recipes are much simpler. They are simply callable objects that accept the name of the part to be uninstalled and the part’s options dictionary. Uninstall recipes don’t have access to the part itself since it maybe not be able to be instantiated at uninstallation time.

Here’s a recipe that simulates installation of a system service, along with an uninstall recipe that simulates removing the service.

    >>> write(sample_buildout, 'recipes', 'service.py',
    ... """
    ... import sys
    ... class Service:
    ...
    ...     def __init__(self, buildout, name, options):
    ...         self.buildout = buildout
    ...         self.name = name
    ...         self.options = options
    ...
    ...     def install(self):
    ...         sys.stdout.write("chkconfig --add %s\\n"
    ...                          % self.options['script'])
    ...         return ()
    ...
    ...     def update(self):
    ...         pass
    ...
    ...
    ... def uninstall_service(name, options):
    ...     sys.stdout.write("chkconfig --del %s\\n" % options['script'])
    ... """)

To use these recipes we must register them using entry points. Make sure to use the same name for the recipe and uninstall recipe. This is required to let buildout know which uninstall recipe goes with which recipe.

    >>> write(sample_buildout, 'recipes', 'setup.py',
    ... """
    ... from setuptools import setup
    ... entry_points = (
    ... '''
    ... [zc.buildout]
    ... mkdir = mkdir:Mkdir
    ... debug = debug:Debug
    ... service = service:Service
    ...
    ... [zc.buildout.uninstall]
    ... service = service:uninstall_service
    ... ''')
    ... setup(name="recipes", entry_points=entry_points)
    ... """)

Here’s how these recipes could be used in a buildout:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = service
    ...
    ... [service]
    ... recipe = recipes:service
    ... script = /path/to/script
    ... """)

When the buildout is run the service will be installed

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Installing service.
    chkconfig --add /path/to/script

The service has been installed. If the buildout is run again with no changes, the service shouldn’t be changed.

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Updating service.

Now we change the service part to trigger uninstallation and re-installation.

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = service
    ...
    ... [service]
    ... recipe = recipes:service
    ... script = /path/to/a/different/script
    ... """)

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling service.
    Running uninstall recipe.
    chkconfig --del /path/to/script
    Installing service.
    chkconfig --add /path/to/a/different/script

Now we remove the service part, and add another part.

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... """)

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling service.
    Running uninstall recipe.
    chkconfig --del /path/to/a/different/script
    Installing debug.
    recipe recipes:debug

Uninstall recipes don’t have to take care of removing all the files and directories created by the part. This is still done automatically, following the execution of the uninstall recipe. An upshot is that an uninstallation recipe can access files and directories created by a recipe before they are deleted.

For example, here’s an uninstallation recipe that simulates backing up a directory before it is deleted. It is designed to work with the mkdir recipe introduced earlier.

    >>> write(sample_buildout, 'recipes', 'backup.py',
    ... """
    ... import os, sys
    ... def backup_directory(name, options):
    ...     path = options['path']
    ...     size = len(os.listdir(path))
    ...     sys.stdout.write("backing up directory %s of size %s\\n"
    ...                      % (path, size))
    ... """)

It must be registered with the zc.buildout.uninstall entry point. Notice how it is given the name ‘mkdir’ to associate it with the mkdir recipe.

    >>> write(sample_buildout, 'recipes', 'setup.py',
    ... """
    ... from setuptools import setup
    ... entry_points = (
    ... '''
    ... [zc.buildout]
    ... mkdir = mkdir:Mkdir
    ... debug = debug:Debug
    ... service = service:Service
    ...
    ... [zc.buildout.uninstall]
    ... uninstall_service = service:uninstall_service
    ... mkdir = backup:backup_directory
    ... ''')
    ... setup(name="recipes", entry_points=entry_points)
    ... """)

Now we can use it with a mkdir part.

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = dir debug
    ...
    ... [dir]
    ... recipe = recipes:mkdir
    ... path = my_directory
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... """)

Run the buildout to install the part.

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Installing dir.
    dir: Creating directory my_directory
    Installing debug.
    recipe recipes:debug

Now we remove the part from the configuration file.

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... """)

When the buildout is run the part is removed, and the uninstall recipe is run before the directory is deleted.

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling dir.
    Running uninstall recipe.
    backing up directory /sample-buildout/my_directory of size 0
    Updating debug.
    recipe recipes:debug

Now we will return the registration to normal for the benefit of the rest of the examples.

    >>> write(sample_buildout, 'recipes', 'setup.py',
    ... """
    ... from setuptools import setup
    ... entry_points = (
    ... '''
    ... [zc.buildout]
    ... mkdir = mkdir:Mkdir
    ... debug = debug:Debug
    ... ''')
    ... setup(name="recipes", entry_points=entry_points)
    ... """)

## Command-line usage

A number of arguments can be given on the buildout command line. The command usage is:

    buildout [options and assignments] [command [command arguments]]

The following options are supported:

-h (or –help)
  Print basic usage information. If this option is used, then all other options are ignored.

`-c filename` | The -c option can be used to specify a configuration file, rather than buildout.cfg in the current directory.
`-t socket_timeout`
| Specify the socket timeout in seconds.
`-v` | Increment the verbosity by 10. The verbosity is used to adjust the logging level. The verbosity is subtracted from the numeric value of the log-level option specified in the configuration file.
`-q` | Decrement the verbosity by 10.
`-U` | Don’t read user-default configuration.
`-o` | Run in off-line mode. This is equivalent to the assignment buildout:offline=true.
`-O` | Run in non-off-line mode. This is equivalent to the assignment buildout:offline=false. This is the default buildout mode. The -O option would normally be used to override a true offline setting in a configuration file.
`-n` | Run in newest mode. This is equivalent to the assignment buildout:newest=true. With this setting, which is the default, buildout will try to find the newest versions of distributions available that satisfy its requirements.
`-N` | Run in non-newest mode. This is equivalent to the assignment buildout:newest=false. With this setting, buildout will not seek new distributions if installed distributions satisfy it’s requirements.

Assignments are of the form:

    section_name:option_name=value

Or:

    option_name=value

which is equivalent to:

    buildout:option_name=value

Options and assignments can be given in any order.

Here’s an example:

    >>> write(sample_buildout, 'other.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug
    ... installed = .other.cfg
    ... log-level = WARNING
    ...
    ... [debug]
    ... name = other
    ... recipe = recipes:debug
    ... """)

Note that we used the installed buildout option to specify an alternate file to store information about installed parts.

    >>> print_(system(buildout+' -c other.cfg debug:op1=foo -v'), end='')
    Develop: '/sample-buildout/recipes'
    Installing debug.
    name other
    op1 foo
    recipe recipes:debug

Here we used the -c option to specify an alternate configuration file, and the -v option to increase the level of logging from the default, WARNING.

Options can also be combined in the usual Unix way, as in:

    >>> print_(system(buildout+' -vcother.cfg debug:op1=foo'), end='')
    Develop: '/sample-buildout/recipes'
    Updating debug.
    name other
    op1 foo
    recipe recipes:debug

Here we combined the -v and -c options with the configuration file name. Note that the -c option has to be last, because it takes an argument.

    >>> os.remove(os.path.join(sample_buildout, 'other.cfg'))
    >>> os.remove(os.path.join(sample_buildout, '.other.cfg'))

The most commonly used command is ‘install’ and it takes a list of parts to install. if any parts are specified, only those parts are installed. To illustrate this, we’ll update our configuration and run the buildout in the usual way:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug d1 d2 d3
    ...
    ... [d1]
    ... recipe = recipes:mkdir
    ... path = d1
    ...
    ... [d2]
    ... recipe = recipes:mkdir
    ... path = d2
    ...
    ... [d3]
    ... recipe = recipes:mkdir
    ... path = d3
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... """)

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling debug.
    Installing debug.
    recipe recipes:debug
    Installing d1.
    d1: Creating directory d1
    Installing d2.
    d2: Creating directory d2
    Installing d3.
    d3: Creating directory d3

    >>> ls(sample_buildout)
    -  .installed.cfg
    -  b1.cfg
    -  b2.cfg
    -  base.cfg
    d  bin
    -  buildout.cfg
    d  d1
    d  d2
    d  d3
    d  demo
    d  develop-eggs
    d  eggs
    d  parts
    d  recipes

    >>> cat(sample_buildout, '.installed.cfg')
    ...
    [buildout]
    installed_develop_eggs = /sample-buildout/develop-eggs/recipes.egg-link
    parts = debug d1 d2 d3

    [debug]
    __buildout_installed__ =
    __buildout_signature__ = recipes-PiIFiO8ny5yNZ1S3JfT0xg==
    recipe = recipes:debug

    [d1]
    __buildout_installed__ = /sample-buildout/d1
    __buildout_signature__ = recipes-PiIFiO8ny5yNZ1S3JfT0xg==
    path = /sample-buildout/d1
    recipe = recipes:mkdir

    [d2]
    __buildout_installed__ = /sample-buildout/d2
    __buildout_signature__ = recipes-PiIFiO8ny5yNZ1S3JfT0xg==
    path = /sample-buildout/d2
    recipe = recipes:mkdir

    [d3]
    __buildout_installed__ = /sample-buildout/d3
    __buildout_signature__ = recipes-PiIFiO8ny5yNZ1S3JfT0xg==
    path = /sample-buildout/d3
    recipe = recipes:mkdir

Now we’ll update our configuration file:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug d2 d3 d4
    ...
    ... [d2]
    ... recipe = recipes:mkdir
    ... path = data2
    ...
    ... [d3]
    ... recipe = recipes:mkdir
    ... path = data3
    ...
    ... [d4]
    ... recipe = recipes:mkdir
    ... path = ${d2:path}-extra
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... x = 1
    ... """)

and run the buildout specifying just d3 and d4:

    >>> print_(system(buildout+' install d3 d4'), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling d3.
    Installing d3.
    d3: Creating directory data3
    Installing d4.
    d4: Creating directory data2-extra

    >>> ls(sample_buildout)
    -  .installed.cfg
    -  b1.cfg
    -  b2.cfg
    -  base.cfg
    d  bin
    -  buildout.cfg
    d  d1
    d  d2
    d  data2-extra
    d  data3
    d  demo
    d  develop-eggs
    d  eggs
    d  parts
    d  recipes

Only the d3 and d4 recipes ran. d3 was removed and data3 and data2-extra were created.

The .installed.cfg is only updated for the recipes that ran:

    >>> cat(sample_buildout, '.installed.cfg')
    ...
    [buildout]
    installed_develop_eggs = /sample-buildout/develop-eggs/recipes.egg-link
    parts = debug d1 d2 d3 d4

    [debug]
    __buildout_installed__ =
    __buildout_signature__ = recipes-PiIFiO8ny5yNZ1S3JfT0xg==
    recipe = recipes:debug

    [d1]
    __buildout_installed__ = /sample-buildout/d1
    __buildout_signature__ = recipes-PiIFiO8ny5yNZ1S3JfT0xg==
    path = /sample-buildout/d1
    recipe = recipes:mkdir

    [d2]
    __buildout_installed__ = /sample-buildout/d2
    __buildout_signature__ = recipes-PiIFiO8ny5yNZ1S3JfT0xg==
    path = /sample-buildout/d2
    recipe = recipes:mkdir

    [d3]
    __buildout_installed__ = /sample-buildout/data3
    __buildout_signature__ = recipes-PiIFiO8ny5yNZ1S3JfT0xg==
    path = /sample-buildout/data3
    recipe = recipes:mkdir

    [d4]
    __buildout_installed__ = /sample-buildout/data2-extra
    __buildout_signature__ = recipes-PiIFiO8ny5yNZ1S3JfT0xg==
    path = /sample-buildout/data2-extra
    recipe = recipes:mkdir

Note that the installed data for debug, d1, and d2 haven’t changed, because we didn’t install those parts and that the d1 and d2 directories are still there.

Now, if we run the buildout without the install command:

    >>> print_(system(buildout), end='')
    Develop: '/sample-buildout/recipes'
    Uninstalling d2.
    Uninstalling d1.
    Uninstalling debug.
    Installing debug.
    recipe recipes:debug
    x 1
    Installing d2.
    d2: Creating directory data2
    Updating d3.
    Updating d4.

We see the output of the debug recipe and that data2 was created. We also see that d1 and d2 have gone away:

    >>> ls(sample_buildout)
    -  .installed.cfg
    -  b1.cfg
    -  b2.cfg
    -  base.cfg
    d  bin
    -  buildout.cfg
    d  data2
    d  data2-extra
    d  data3
    d  demo
    d  develop-eggs
    d  eggs
    d  parts
    d  recipes

## Alternate directory and file locations

The buildout normally puts the bin, eggs, and parts directories in the directory in the directory containing the configuration file. You can provide alternate locations, and even names for these directories.

    >>> alt = tmpdir('sample-alt')

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts =
    ... develop-eggs-directory = %(developbasket)s
    ... eggs-directory = %(basket)s
    ... bin-directory = %(scripts)s
    ... parts-directory = %(work)s
    ... """ % dict(
    ...    developbasket = os.path.join(alt, 'developbasket'),
    ...    basket = os.path.join(alt, 'basket'),
    ...    scripts = os.path.join(alt, 'scripts'),
    ...    work = os.path.join(alt, 'work'),
    ... ))

    >>> print_(system(buildout), end='')
    Creating directory '/sample-alt/scripts'.
    Creating directory '/sample-alt/work'.
    Creating directory '/sample-alt/basket'.
    Creating directory '/sample-alt/developbasket'.
    Develop: '/sample-buildout/recipes'
    Uninstalling d4.
    Uninstalling d3.
    Uninstalling d2.
    Uninstalling debug.

    >>> ls(alt)
    d  basket
    d  developbasket
    d  scripts
    d  work

    >>> ls(alt, 'developbasket')
    -  recipes.egg-link

You can also specify an alternate buildout directory:

    >>> rmdir(alt)
    >>> alt = tmpdir('sample-alt')

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... directory = %(alt)s
    ... develop = %(recipes)s
    ... parts =
    ... """ % dict(
    ...    alt=alt,
    ...    recipes=os.path.join(sample_buildout, 'recipes'),
    ...    ))

    >>> print_(system(buildout), end='')
    Creating directory '/sample-alt/bin'.
    Creating directory '/sample-alt/parts'.
    Creating directory '/sample-alt/eggs'.
    Creating directory '/sample-alt/develop-eggs'.
    Develop: '/sample-buildout/recipes'

    >>> ls(alt)
    -  .installed.cfg
    d  bin
    d  develop-eggs
    d  eggs
    d  parts

    >>> ls(alt, 'develop-eggs')
    -  recipes.egg-link

## Logging control

Three buildout options are used to control logging:

log-level
  specifies the log level
verbosity
  adjusts the log level
log-format
  allows an alternate logging for mat to be specified

We’ve already seen the log level and verbosity. Let’s look at an example of changing the format:

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts =
    ... log-level = 25
    ... verbosity = 5
    ... log-format = %(levelname)s %(message)s
    ... """)

Here, we’ve changed the format to include the log-level name, rather than the logger name.

We’ve also illustrated, with a contrived example, that the log level can be a numeric value and that the verbosity can be specified in the configuration file. Because the verbosity is subtracted from the log level, we get a final log level of 20, which is the INFO level.

    >>> print_(system(buildout), end='')
    INFO Develop: '/sample-buildout/recipes'

## Predefined buildout options

Buildouts have a number of predefined options that recipes can use and that users can override in their configuration files. To see these, we’ll run a minimal buildout configuration with a debug logging level. One of the features of debug logging is that the configuration database is shown.

    >>> write(sample_buildout, 'buildout.cfg',
    ... """
    ... [buildout]
    ... parts =
    ... """)

    >>> print_(system(buildout+' -vv'), end='')
    Installing 'zc.buildout', 'setuptools'.
    We have a develop egg: zc.buildout 1.0.0.
    We have the best distribution that satisfies 'setuptools'.
    Picked: setuptools = 0.7

    Configuration data:
    [buildout]
    allow-hosts = *
    allow-picked-versions = true
    bin-directory = /sample-buildout/bin
    develop-eggs-directory = /sample-buildout/develop-eggs
    directory = /sample-buildout
    eggs-directory = /sample-buildout/eggs
    executable = python
    find-links =
    install-from-cache = false
    installed = /sample-buildout/.installed.cfg
    log-format =
    log-level = INFO
    newest = true
    offline = false
    parts =
    parts-directory = /sample-buildout/parts
    prefer-final = true
    python = buildout
    show-picked-versions = false
    socket-timeout =
    update-versions-file =
    use-dependency-links = true
    verbosity = 20
    versions = versions
    [versions]
    zc.buildout = >=1.99
    zc.recipe.egg = >=1.99

All of these options can be overridden by configuration files or by command-line assignments. We’ve discussed most of these options already, but let’s review them and touch on some we haven’t discussed:

allow-hosts

  On some environments the links visited by zc.buildout can be forbidden by paranoid firewalls. These URLs might be in the chain of links visited by zc.buildout as defined by buildout’s find-links option, or as defined by various eggs in their url, download_url, dependency_links metadata.

  The fact that package_index works like a spider and might visit links and go to other locations makes this even harder.

  The allow-hosts option provides a way to prevent this, and works exactly like the one provided in easy_install.

  You can provide a list of allowed host, together with wildcards:

      [buildout]
      ...

      allow-hosts =
          *.python.org
          example.com

  All URLs that does not match these hosts will not be visited.

allow-picked-versions
  By default, the buildout will choose the best match for a given requirement if the requirement is not specified precisely (for instance, using the “versions” option. This behavior corresponds to the “allow-picked-versions” being set to its default value, “true”. If “allow-picked-versions” is “false,” instead of picking the best match, buildout will raise an error. This helps enforce repeatability.
bin-directory
  The directory path where scripts are written. This can be a relative path, which is interpreted relative to the directory option.
develop-eggs-directory
  The directory path where development egg links are created for software being created in the local project. This can be a relative path, which is interpreted relative to the directory option.
directory
  The buildout directory. This is the base for other buildout file and directory locations, when relative locations are used.
eggs-directory
  The directory path where downloaded eggs are put. It is common to share this directory across buildouts. Eggs in this directory should never be modified. This can be a relative path, which is interpreted relative to the directory option.
find-links

  You can specify more locations to search for distributions using the find-links option. All locations specified will be searched for distributions along with the package index as described before.

  Locations can be urls:

      [buildout]
      ...
      find-links = http://download.zope.org/distribution/

  They can also be directories on disk:

      [buildout]
      ...
      find-links = /some/path

  Finally, they can also be direct paths to distributions:

      [buildout]
      ...
      find-links = /some/path/someegg-1.0.0-py2.3.egg

  Any number of locations can be specified in the find-links option:

      [buildout]
      ...
      find-links =
          http://download.zope.org/distribution/
          /some/otherpath
          /some/path/someegg-1.0.0-py2.3.egg

install-from-cache
  A download cache can be used as the basis of application source releases. In an application source release, we want to distribute an application that can be built without making any network accesses. In this case, we distribute a buildout with download cache and tell the buildout to install from the download cache only, without making network accesses. The buildout install-from-cache option can be used to signal that packages should be installed only from the download cache.
installed
  The file path where information about the results of the previous buildout run is written. This can be a relative path, which is interpreted relative to the directory option. This file provides an inventory of installed parts with information needed to decide which if any parts need to be uninstalled.
log-format
  The format used for logging messages.
log-level
  The log level before verbosity adjustment
newest
  By default buildout and recipes will try to find the newest versions of distributions needed to satisfy requirements. This can be very time consuming, especially when incrementally working on setting up a buildout or working on a recipe. The buildout “newest” option can be used to to suppress this. If the “newest” option is set to false, then new distributions won’t be sought if an installed distribution meets requirements. The “newest” option can also be set to false using the -N command-line option. See also the “offline” option.
offline
  The “offline” option goes a bit further than the “newest” option. If the buildout “offline” option is given a value of “true”, the buildout and recipes that are aware of the option will avoid doing network access. This is handy when running the buildout when not connected to the internet. It also makes buildouts run much faster. This option is typically set using the buildout -o option.
parts
  A white space separated list of parts to be installed.
parts-directory
  A working directory that parts can used to store data.
prefer-final

  Currently, when searching for new releases, the newest available release is used. This isn’t usually ideal, as you may get a development release or alpha releases not ready to be widely used. You can request that final releases be preferred using the prefer final option in the buildout section:

      [buildout]
      ...
      prefer-final = true

  When the prefer-final option is set to true, then when searching for new releases, final releases are preferred. If there are final releases that satisfy distribution requirements, then those releases are used even if newer non-final releases are available. The buildout prefer-final option can be used to override this behavior.

  In buildout version 2, final releases will be preferred by default. You will then need to use a false value for prefer-final to get the newest releases.

use-dependency-links

  By default buildout will obey the setuptools dependency_links metadata when it looks for dependencies. This behavior can be controlled with the use-dependency-links buildout option:

      [buildout]
      ...
      use-dependency-links = false

  The option defaults to true. If you set it to false, then dependency links are only looked for in the locations specified by find-links.

verbosity
  A log-level adjustment. Typically, this is set via the -q and -v command-line options.

## Creating new buildouts and bootstrapping

If zc.buildout is installed, you can use it to create a new buildout with it’s own local copies of zc.buildout and setuptools and with local buildout scripts.

    >>> sample_bootstrapped = tmpdir('sample-bootstrapped')

    >>> print_(system(buildout
    ...              +' -c'+os.path.join(sample_bootstrapped, 'setup.cfg')
    ...              +' init'), end='')
    Creating '/sample-bootstrapped/setup.cfg'.
    Creating directory '/sample-bootstrapped/bin'.
    Creating directory '/sample-bootstrapped/parts'.
    Creating directory '/sample-bootstrapped/eggs'.
    Creating directory '/sample-bootstrapped/develop-eggs'.
    Generated script '/sample-bootstrapped/bin/buildout'.

Note that a basic setup.cfg was created for us. This is because we provided an ‘init’ argument. By default, the generated `setup.cfg` is as minimal as it could be:

    >>> cat(sample_bootstrapped, 'setup.cfg')
    [buildout]
    parts =

We also get other buildout artifacts:

    >>> ls(sample_bootstrapped)
    d  bin
    d  develop-eggs
    d  eggs
    d  parts
    -  setup.cfg

    >>> ls(sample_bootstrapped, 'bin')
    -  buildout

    >>> _ = (ls(sample_bootstrapped, 'eggs'),
    ...      ls(sample_bootstrapped, 'develop-eggs'))
    -  setuptools-0.7-py2.3.egg
    -  zc.buildout-1.0-py2.3.egg

(We list both the eggs and develop-eggs directories because the buildout or setuptools egg could be installed in the develop-eggs directory if the original buildout had develop eggs for either buildout or setuptools.)

Note that the buildout script was installed but not run. To run the buildout, we’d have to run the installed buildout script.

If we have an existing buildout that already has a buildout.cfg, we’ll normally use the bootstrap command instead of init. It will complain if there isn’t a configuration file:

    >>> sample_bootstrapped2 = tmpdir('sample-bootstrapped2')

    >>> print_(system(buildout
    ...              +' -c'+os.path.join(sample_bootstrapped2, 'setup.cfg')
    ...              +' bootstrap'), end='')
    While:
      Initializing.
    Error: Couldn't open /sample-bootstrapped2/setup.cfg

    >>> write(sample_bootstrapped2, 'setup.cfg',
    ... """
    ... [buildout]
    ... parts =
    ... """)

    >>> print_(system(buildout
    ...              +' -c'+os.path.join(sample_bootstrapped2, 'setup.cfg')
    ...              +' bootstrap'), end='')
    Creating directory '/sample-bootstrapped2/bin'.
    Creating directory '/sample-bootstrapped2/parts'.
    Creating directory '/sample-bootstrapped2/eggs'.
    Creating directory '/sample-bootstrapped2/develop-eggs'.
    Generated script '/sample-bootstrapped2/bin/buildout'.

Similarly, if there is a configuration file and we use the init command, we’ll get an error that the configuration file already exists:

    >>> print_(system(buildout
    ...              +' -c'+os.path.join(sample_bootstrapped, 'setup.cfg')
    ...              +' init'), end='')
    While:
      Initializing.
    Error: '/sample-bootstrapped/setup.cfg' already exists.

## Initial eggs

When using the `init` command, you can specify distribution requirements or paths to use:

    >>> cd(sample_bootstrapped)
    >>> remove('setup.cfg')
    >>> print_(system(buildout + ' -csetup.cfg init demo other ./src'), end='')
    Creating '/sample-bootstrapped/setup.cfg'.
    Getting distribution for 'zc.recipe.egg>=2.0.0a3'.
    Got zc.recipe.egg
    Installing py.
    Getting distribution for 'demo'.
    Got demo 0.3.
    Getting distribution for 'other'.
    Got other 1.0.
    Getting distribution for 'demoneeded'.
    Got demoneeded 1.1.
    Generated script '/sample-bootstrapped/bin/demo'.
    Generated script '/sample-bootstrapped/bin/distutilsscript'.
    Generated interpreter '/sample-bootstrapped/bin/py'.

This causes a `py` part to be included that sets up a custom python interpreter with the given requirements or paths:

    >>> cat('setup.cfg')
    [buildout]
    parts = py

    [py]
    recipe = zc.recipe.egg
    interpreter = py
    eggs =
      demo
      other
    extra-paths =
      ./src

Passing requirements or paths causes the the buildout to be run as part of initialization. In the example above, we got a number of distributions installed and 2 scripts generated. The first, `demo`, was defined by the `demo` project. The second, `py` was defined by the generated configuration. It’s a “custom interpreter” that behaves like a standard Python interpreter, except that includes the specified eggs and extra paths in it’s Python path.

We specified a source directory that didn’t exist. Buildout created it for us:

    >>> ls('.')
    -  .installed.cfg
    d  bin
    d  develop-eggs
    d  eggs
    d  parts
    -  setup.cfg
    d  src

    >>> uncd()

## Finding distributions

By default, buildout searches the Python Package Index when looking for distributions. You can, instead, specify your own index to search using the index option:

    [buildout]
    ...
    index = http://index.example.com/

This index, or the default of http://pypi.python.org/simple/ if no index is specified, will always be searched for distributions unless running buildout with options that prevent searching for distributions. The latest version of the distribution that meets the requirements of the buildout will always be used.

You can also specify more locations to search for distributions using the find-links option. See its description above.

## Controlling the installation database

The buildout installed option is used to specify the file used to save information on installed parts. This option is initialized to ”.installed.cfg”, but it can be overridden in the configuration file or on the command line:

    >>> write('buildout.cfg',
    ... """
    ... [buildout]
    ... develop = recipes
    ... parts = debug
    ...
    ... [debug]
    ... recipe = recipes:debug
    ... """)

    >>> print_(system(buildout+' buildout:installed=inst.cfg'), end='')
    Develop: '/sample-buildout/recipes'
    Installing debug.
    recipe recipes:debug

    >>> ls(sample_buildout)
    -  b1.cfg
    -  b2.cfg
    -  base.cfg
    d  bin
    -  buildout.cfg
    d  demo
    d  develop-eggs
    d  eggs
    -  inst.cfg
    d  parts
    d  recipes

The installation database can be disabled by supplying an empty buildout installed option:

    >>> os.remove('inst.cfg')
    >>> print_(system(buildout+' buildout:installed='), end='')
    Develop: '/sample-buildout/recipes'
    Installing debug.
    recipe recipes:debug

    >>> ls(sample_buildout)
    -  b1.cfg
    -  b2.cfg
    -  base.cfg
    d  bin
    -  buildout.cfg
    d  demo
    d  develop-eggs
    d  eggs
    d  parts
    d  recipes

Note that there will be no installation database if there are no parts:

    >>> write('buildout.cfg',
    ... """
    ... [buildout]
    ... parts =
    ... """)

    >>> print_(system(buildout+' buildout:installed=inst.cfg'), end='')

    >>> ls(sample_buildout)
    -  b1.cfg
    -  b2.cfg
    -  base.cfg
    d  bin
    -  buildout.cfg
    d  demo
    d  develop-eggs
    d  eggs
    d  parts
    d  recipes

## Extensions

A feature allows code to be loaded and run after configuration files have been read but before the buildout has begun any processing. The intent is to allow special plugins such as urllib2 request handlers to be loaded.

To load an extension, we use the extensions option and list one or more distribution requirements, on separate lines. The distributions named will be loaded and any `zc.buildout.extension` entry points found will be called with the buildout as an argument. When buildout finishes processing, any `zc.buildout.unloadextension` entry points found will be called with the buildout as an argument.

Let’s create a sample extension in our sample buildout created in the previous section:

    >>> mkdir(sample_bootstrapped, 'demo')

    >>> write(sample_bootstrapped, 'demo', 'demo.py',
    ... """
    ... import sys
    ... def ext(buildout):
    ...     sys.stdout.write('%s %s\\n' % ('ext', sorted(buildout)))
    ... def unload(buildout):
    ...     sys.stdout.write('%s %s\\n' % ('unload', sorted(buildout)))
    ... """)

    >>> write(sample_bootstrapped, 'demo', 'setup.py',
    ... """
    ... from setuptools import setup
    ...
    ... setup(
    ...     name = "demo",
    ...     entry_points = {
    ...        'zc.buildout.extension': ['ext = demo:ext'],
    ...        'zc.buildout.unloadextension': ['ext = demo:unload'],
    ...        },
    ...     )
    ... """)

Our extension just prints out the word ‘demo’, and lists the sections found in the buildout passed to it.

We’ll update our buildout.cfg to list the demo directory as a develop egg to be built:

    >>> write(sample_bootstrapped, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = demo
    ... parts =
    ... """)

    >>> os.chdir(sample_bootstrapped)
    >>> print_(system(os.path.join(sample_bootstrapped, 'bin', 'buildout')),
    ...        end='')
    Develop: '/sample-bootstrapped/demo'

Now we can add the extensions option. We were a bit tricky and ran the buildout once with the demo develop egg defined but without the extension option. This is because extensions are loaded before the buildout creates develop eggs. We needed to use a separate buildout run to create the develop egg. Normally, when eggs are loaded from the network, we wouldn’t need to do anything special.

    >>> write(sample_bootstrapped, 'buildout.cfg',
    ... """
    ... [buildout]
    ... develop = demo
    ... extensions = demo
    ... parts =
    ... """)

We see that our extension is loaded and executed:

    >>> print_(system(os.path.join(sample_bootstrapped, 'bin', 'buildout')),
    ...        end='')
    ext ['buildout', 'versions']
    Develop: '/sample-bootstrapped/demo'
    unload ['buildout', 'versions']