10. Full Grammar specification — Python 3.6.15 documentation (original) (raw)

This is the full Python grammar, as it is read by the parser generator and used to parse Python source files:

Grammar for Python

NOTE WELL: You should also follow all the steps listed at

https://devguide.python.org/grammar/

Start symbols for the grammar:

single_input is a single interactive statement;

file_input is a module or sequence of commands read from an input file;

eval_input is the input for the eval() functions.

NB: compound_stmt in single_input is followed by extra NEWLINE!

single_input: NEWLINE | simple_stmt | compound_stmt NEWLINE file_input: (NEWLINE | stmt)* ENDMARKER eval_input: testlist NEWLINE* ENDMARKER

decorator: '@' dotted_name [ '(' [arglist] ')' ] NEWLINE decorators: decorator+ decorated: decorators (classdef | funcdef | async_funcdef)

async_funcdef: ASYNC funcdef funcdef: 'def' NAME parameters ['->' test] ':' suite

parameters: '(' [typedargslist] ')' typedargslist: (tfpdef ['=' test] (',' tfpdef ['=' test])* [',' [ '' [tfpdef] (',' tfpdef ['=' test]) [',' ['' tfpdef [',']]] | '' tfpdef [',']]] | '' [tfpdef] (',' tfpdef ['=' test]) [',' ['' tfpdef [',']]] | '' tfpdef [',']) tfpdef: NAME [':' test] varargslist: (vfpdef ['=' test] (',' vfpdef ['=' test])* [',' [ '' [vfpdef] (',' vfpdef ['=' test]) [',' ['' vfpdef [',']]] | '' vfpdef [',']]] | '' [vfpdef] (',' vfpdef ['=' test]) [',' ['' vfpdef [',']]] | '' vfpdef [','] ) vfpdef: NAME

stmt: simple_stmt | compound_stmt simple_stmt: small_stmt (';' small_stmt)* [';'] NEWLINE small_stmt: (expr_stmt | del_stmt | pass_stmt | flow_stmt | import_stmt | global_stmt | nonlocal_stmt | assert_stmt) expr_stmt: testlist_star_expr (annassign | augassign (yield_expr|testlist) | ('=' (yield_expr|testlist_star_expr))) annassign: ':' test ['=' test] testlist_star_expr: (test|star_expr) (',' (test|star_expr)) [','] augassign: ('+=' | '-=' | '*=' | '@=' | '/=' | '%=' | '&=' | '|=' | '^=' | '<<=' | '>>=' | '**=' | '//=')

For normal and annotated assignments, additional restrictions enforced by the interpreter

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]] import_stmt: import_name | import_from import_name: 'import' dotted_as_names

note below: the ('.' | '...') is necessary because '...' is tokenized as ELLIPSIS

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' NAME (',' NAME)* nonlocal_stmt: 'nonlocal' NAME (',' NAME)* assert_stmt: 'assert' test [',' test]

compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt | with_stmt | funcdef | classdef | decorated | async_stmt async_stmt: ASYNC (funcdef | with_stmt | for_stmt) 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' with_item (',' with_item)* ':' suite with_item: test ['as' expr]

NB compile.c makes sure that the default except clause is last

except_clause: 'except' [test ['as' NAME]] suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT

test: or_test ['if' or_test 'else' test] | lambdef test_nocond: or_test | lambdef_nocond lambdef: 'lambda' [varargslist] ':' test lambdef_nocond: 'lambda' [varargslist] ':' test_nocond 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)*

<> isn't actually a valid comparison operator in Python. It's here for the

sake of a future import described in PEP 401 (which really works :-)

comp_op: '<'|'>'|'=='|'>='|'<='|'<>'|'!='|'in'|'not' 'in'|'is'|'is' 'not' star_expr: '' expr 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_expr ['' factor] atom_expr: [AWAIT] atom trailer atom: ('(' [yield_expr|testlist_comp] ')' | '[' [testlist_comp] ']' | '{' [dictorsetmaker] '}' | NAME | NUMBER | STRING+ | '...' | 'None' | 'True' | 'False') testlist_comp: (test|star_expr) ( comp_for | (',' (test|star_expr)) [','] ) trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME subscriptlist: subscript (',' subscript)* [','] subscript: test | [test] ':' [test] [sliceop] sliceop: ':' [test] exprlist: (expr|star_expr) (',' (expr|star_expr))* [','] testlist: test (',' test)* [','] dictorsetmaker: ( ((test ':' test | '' expr) (comp_for | (',' (test ':' test | '' expr))* [','])) | ((test | star_expr) (comp_for | (',' (test | star_expr))* [','])) )

classdef: 'class' NAME ['(' [arglist] ')'] ':' suite

arglist: argument (',' argument)* [',']

The reason that keywords are test nodes instead of NAME is that using NAME

results in an ambiguity. ast.c makes sure it's a NAME.

"test '=' test" is really "keyword '=' test", but we have no such token.

These need to be in a single rule to avoid grammar that is ambiguous

to our LL(1) parser. Even though 'test' includes '*expr' in star_expr,

we explicitly match '*' here, too, to give it proper precedence.

Illegal combinations and orderings are blocked in ast.c:

multiple (test comp_for) arguments are blocked; keyword unpackings

that precede iterable unpackings are blocked; etc.

argument: ( test [comp_for] | test '=' test | '**' test | '*' test )

comp_iter: comp_for | comp_if comp_for: [ASYNC] 'for' exprlist 'in' or_test [comp_iter] comp_if: 'if' test_nocond [comp_iter]

not used in grammar, but may appear in "node" passed from Parser to Compiler

encoding_decl: NAME

yield_expr: 'yield' [yield_arg] yield_arg: 'from' test | testlist