# Grammar for Python

# Note: Changing the grammar specified in this file will most likely # require corresponding changes in the parser module # (../Modules/parsermodule.c). If you can’t make the changes to # that module yourself, please co-ordinate the required changes # with someone who can; ask around on python-dev for help. Fred # Drake <fdrake@acm.org> will probably be listening there.

# NOTE WELL: You should also follow all the steps listed in PEP 306, # “How to Change Python’s Grammar”

# Commands for Kees Blom’s railroad program #diagram:token NAME #diagram:token NUMBER #diagram:token STRING #diagram:token NEWLINE #diagram:token ENDMARKER #diagram:token INDENT #diagram:outputinput python.bla #diagram:token DEDENT #diagram:outputtextwidth 20.04cmoddsidemargin 0.0cmevensidemargin 0.0cm #diagram:rules

# Start symbols for the grammar: # file_input is a module or sequence of commands read from an input file; # single_input is a single interactive statement; # eval_input is the input for the eval() and input() functions. # NB: compound_stmt in single_input is followed by extra NEWLINE! file_input: (NEWLINE | stmt)* ENDMARKER single_input: NEWLINE | simple_stmt | compound_stmt NEWLINE eval_input: testlist NEWLINE* ENDMARKER

decorator: ‘@’ dotted_name [ ‘(‘ [arglist] ‘)’ ] NEWLINE decorators: decorator+ decorated: decorators (classdef | funcdef) funcdef: ‘def’ NAME parameters [‘->’ test] ‘:’ suite parameters: ‘(‘ [typedargslist] ‘)’ typedargslist: ((tfpdef [‘=’ test] ‘,’)*

> (‘*’ [tname] (‘,’ tname [‘=’ test])* [‘,’ ‘**’ tname] | ‘**’ tname) | tfpdef [‘=’ test] (‘,’ tfpdef [‘=’ test])* [‘,’])

tname: NAME [‘:’ test] tfpdef: tname | ‘(‘ tfplist ‘)’ tfplist: tfpdef (‘,’ tfpdef)* [‘,’] varargslist: ((vfpdef [‘=’ test] ‘,’)*

> (‘*’ [vname] (‘,’ vname [‘=’ test])* [‘,’ ‘**’ vname] | ‘**’ vname) | vfpdef [‘=’ test] (‘,’ vfpdef [‘=’ test])* [‘,’])

vname: NAME vfpdef: vname | ‘(‘ vfplist ‘)’ vfplist: vfpdef (‘,’ vfpdef)* [‘,’]

stmt: simple_stmt | compound_stmt simple_stmt: small_stmt (‘;’ small_stmt)* [‘;’] NEWLINE small_stmt: (expr_stmt | print_stmt | del_stmt | pass_stmt | flow_stmt |

> import_stmt | global_stmt | exec_stmt | assert_stmt)

expr_stmt: testlist (augassign (yield_expr|testlist) |
  (‘=’ (yield_expr|testlist))*)
augassign: (‘+=’ | ‘-=’ | ‘*=’ | ‘/=’ | ‘%=’ | ‘&=’ | ‘|=’ | ‘^=’ |
  ‘<<=’ | ‘>>=’ | ‘**=’ | ‘//=’)

# For normal assignments, additional restrictions enforced by the interpreter print_stmt: ‘print’ ( [ test (‘,’ test)* [‘,’] ] |

> ‘>>’ test [ (‘,’ test)+ [‘,’] ] )

del_stmt: ‘del’ exprlist pass_stmt: ‘pass’ flow_stmt: break_stmt | continue_stmt | return_stmt | raise_stmt | yield_stmt break_stmt: ‘break’ continue_stmt: ‘continue’ return_stmt: ‘return’ [testlist] yield_stmt: yield_expr raise_stmt: ‘raise’ [test [‘from’ test | ‘,’ test [‘,’ test]]] import_stmt: import_name | import_from import_name: ‘import’ dotted_as_names import_from: (‘from’ (‘.’* dotted_name | ‘.’+)

> ‘import’ (‘*’ | ‘(‘ import_as_names ‘)’ | import_as_names))

import_as_name: NAME [‘as’ NAME] dotted_as_name: dotted_name [‘as’ NAME] import_as_names: import_as_name (‘,’ import_as_name)* [‘,’] dotted_as_names: dotted_as_name (‘,’ dotted_as_name)* dotted_name: NAME (‘.’ NAME)* global_stmt: (‘global’ | ‘nonlocal’) NAME (‘,’ NAME)* exec_stmt: ‘exec’ expr [‘in’ test [‘,’ test]] assert_stmt: ‘assert’ test [‘,’ test]

compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt | with_stmt | funcdef | classdef | decorated if_stmt: ‘if’ test ‘:’ suite (‘elif’ test ‘:’ suite)* [‘else’ ‘:’ suite] while_stmt: ‘while’ test ‘:’ suite [‘else’ ‘:’ suite] for_stmt: ‘for’ exprlist ‘in’ testlist ‘:’ suite [‘else’ ‘:’ suite] try_stmt: (‘try’ ‘:’ suite

> ((except_clause ‘:’ suite)+
>   [‘else’ ‘:’ suite] [‘finally’ ‘:’ suite] |

> ‘finally’ ‘:’ suite))

with_stmt: ‘with’ test [ with_var ] ‘:’ suite with_var: ‘as’ expr # NB compile.c makes sure that the default except clause is last except_clause: ‘except’ [test [(‘,’ | ‘as’) test]] suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT

# Backward compatibility cruft to support: # [ x for x in lambda: True, lambda: False if x() ] # even while also allowing: # lambda x: 5 if x else 2 # (But not a mix of the two) testlist_safe: old_test [(‘,’ old_test)+ [‘,’]] old_test: or_test | old_lambdef old_lambdef: ‘lambda’ [varargslist] ‘:’ old_test

test: or_test [‘if’ or_test ‘else’ test] | lambdef or_test: and_test (‘or’ and_test)* and_test: not_test (‘and’ not_test)* not_test: ‘not’ not_test | comparison comparison: expr (comp_op expr)* comp_op: ‘<’|’>’|’==’|’>=’|’<=’|’<>’|’!=’|’in’|’not’ ‘in’|’is’|’is’ ‘not’ expr: xor_expr (‘|’ xor_expr)* xor_expr: and_expr (‘^’ and_expr)* and_expr: shift_expr (‘&’ shift_expr)* shift_expr: arith_expr ((‘<<’|’>>’) arith_expr)* arith_expr: term ((‘+’|’-‘) term)* term: factor ((‘*’|’/’|’%’|’//’) factor)* factor: (‘+’|’-‘|’~’) factor | power power: atom trailer* [‘**’ factor] atom: (‘(‘ [yield_expr|testlist_gexp] ‘)’ |

> ‘[‘ [listmaker] ‘]’ | ‘{‘ [dictsetmaker] ‘}’ | ‘`’ testlist1 ‘`’ | NAME | NUMBER | STRING+ | ‘.’ ‘.’ ‘.’)

listmaker: test ( comp_for | (‘,’ test)* [‘,’] ) testlist_gexp: test ( comp_for | (‘,’ test)* [‘,’] ) lambdef: ‘lambda’ [varargslist] ‘:’ test trailer: ‘(‘ [arglist] ‘)’ | ‘[‘ subscriptlist ‘]’ | ‘.’ NAME subscriptlist: subscript (‘,’ subscript)* [‘,’] subscript: test | [test] ‘:’ [test] [sliceop] sliceop: ‘:’ [test] exprlist: expr (‘,’ expr)* [‘,’] testlist: test (‘,’ test)* [‘,’] dictsetmaker: ( (test ‘:’ test (comp_for | (‘,’ test ‘:’ test)* [‘,’])) |

> (test (comp_for | (‘,’ test)* [‘,’])) )

classdef: ‘class’ NAME [‘(‘ [arglist] ‘)’] ‘:’ suite

arglist: (argument ‘,’)* (argument [‘,’]
  |‘*’ test (‘,’ argument)* [‘,’ ‘**’ test] |‘**’ test)

argument: test [comp_for] | test ‘=’ test # Really [keyword ‘=’] test

comp_iter: comp_for | comp_if comp_for: ‘for’ exprlist ‘in’ testlist_safe [comp_iter] comp_if: ‘if’ old_test [comp_iter]

testlist1: test (‘,’ test)*

# not used in grammar, but may appear in “node” passed from Parser to Compiler encoding_decl: NAME

yield_expr: ‘yield’ [testlist]