Python：完整的语法规范

傷城~ 2022-11-22 00:10 279阅读 0赞

## Python：完整的语法规范 ##

这是完整的 Python 语法规范，直接提取自用于生成 CPython 解析器的语法 (参见 [Grammar/python.gram][Grammar_python.gram])。 这里显示的版本省略了有关代码生成和错误恢复的细节。

所用的标记法是 [EBNF][] 和 [PEG][] 的混合体。 特别地，`&` 后跟一个符号、形符或带括号的分组来表示正向前视（即要求执行匹配但不会被消耗掉），而 `!` 表示负向前视（即要求 \_不\_ 执行匹配）。 我们使用 `|` 分隔符来表示 PEG 的“有序选择” (在传统 PEG 语法中则写为 `/`)。

# PEG grammar for Python
    
    
    file: [statements] ENDMARKER 
    interactive: statement_newline 
    eval: expressions NEWLINE* ENDMARKER 
    func_type: '(' [type_expressions] ')' '->' expression NEWLINE* ENDMARKER 
    fstring: star_expressions
    
    # type_expressions allow */** but ignore them
    type_expressions:
        | ','.expression+ ',' '*' expression ',' '**' expression 
        | ','.expression+ ',' '*' expression 
        | ','.expression+ ',' '**' expression 
        | '*' expression ',' '**' expression 
        | '*' expression 
        | '**' expression 
        | ','.expression+
    
    statements: statement+ 
    statement: compound_stmt  | simple_stmt
    statement_newline:
        | compound_stmt NEWLINE 
        | simple_stmt
        | NEWLINE 
        | ENDMARKER 
    simple_stmt:
        | small_stmt !';' NEWLINE  # Not needed, there for speedup
        | ';'.small_stmt+ [';'] NEWLINE 
    # NOTE: assignment MUST precede expression, else parsing a simple assignment
    # will throw a SyntaxError.
    small_stmt:
        | assignment
        | star_expressions 
        | return_stmt
        | import_stmt
        | raise_stmt
        | 'pass' 
        | del_stmt
        | yield_stmt
        | assert_stmt
        | 'break' 
        | 'continue' 
        | global_stmt
        | nonlocal_stmt
    compound_stmt:
        | function_def
        | if_stmt
        | class_def
        | with_stmt
        | for_stmt
        | try_stmt
        | while_stmt
    
    # NOTE: annotated_rhs may start with 'yield'; yield_expr must start with 'yield'
    assignment:
        | NAME ':' expression ['=' annotated_rhs ] 
        | ('(' single_target ')' 
             | single_subscript_attribute_target) ':' expression ['=' annotated_rhs ] 
        | (star_targets '=' )+ (yield_expr | star_expressions) !'=' [TYPE_COMMENT] 
        | single_target augassign ~ (yield_expr | star_expressions) 
    augassign:
        | '+=' 
        | '-=' 
        | '*=' 
        | '@=' 
        | '/=' 
        | '%=' 
        | '&=' 
        | '|=' 
        | '^=' 
        | '<<=' 
        | '>>=' 
        | '**=' 
        | '//=' 
    
    global_stmt: 'global' ','.NAME+ 
    nonlocal_stmt: 'nonlocal' ','.NAME+ 
    
    yield_stmt: yield_expr 
    
    assert_stmt: 'assert' expression [',' expression ] 
    
    del_stmt:
        | 'del' del_targets &(';' | NEWLINE) 
    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_from_targets 
        | 'from' ('.' | '...')+ 'import' import_from_targets 
    import_from_targets:
        | '(' import_from_as_names [','] ')' 
        | import_from_as_names !','
        | '*' 
    import_from_as_names:
        | ','.import_from_as_name+ 
    import_from_as_name:
        | NAME ['as' NAME ] 
    dotted_as_names:
        | ','.dotted_as_name+ 
    dotted_as_name:
        | dotted_name ['as' NAME ] 
    dotted_name:
        | dotted_name '.' NAME 
        | NAME
    
    if_stmt:
        | 'if' named_expression ':' block elif_stmt 
        | 'if' named_expression ':' block [else_block] 
    elif_stmt:
        | 'elif' named_expression ':' block elif_stmt 
        | 'elif' named_expression ':' block [else_block] 
    else_block: 'else' ':' block 
    
    while_stmt:
        | 'while' named_expression ':' block [else_block] 
    
    for_stmt:
        | 'for' star_targets 'in' ~ star_expressions ':' [TYPE_COMMENT] block [else_block] 
        | ASYNC 'for' star_targets 'in' ~ star_expressions ':' [TYPE_COMMENT] block [else_block] 
    with_stmt:
        | 'with' '(' ','.with_item+ ','? ')' ':' block 
        | 'with' ','.with_item+ ':' [TYPE_COMMENT] block 
        | ASYNC 'with' '(' ','.with_item+ ','? ')' ':' block 
        | ASYNC 'with' ','.with_item+ ':' [TYPE_COMMENT] block 
    with_item:
        | expression 'as' star_target &(',' | ')' | ':') 
        | expression 
    
    try_stmt:
        | 'try' ':' block finally_block 
        | 'try' ':' block except_block+ [else_block] [finally_block] 
    except_block:
        | 'except' expression ['as' NAME ] ':' block 
        | 'except' ':' block 
    finally_block: 'finally' ':' block 
    
    return_stmt:
        | 'return' [star_expressions] 
    
    raise_stmt:
        | 'raise' expression ['from' expression ] 
        | 'raise' 
    
    function_def:
        | decorators function_def_raw 
        | function_def_raw
    
    function_def_raw:
        | 'def' NAME '(' [params] ')' ['->' expression ] ':' [func_type_comment] block 
        | ASYNC 'def' NAME '(' [params] ')' ['->' expression ] ':' [func_type_comment] block 
    func_type_comment:
        | NEWLINE TYPE_COMMENT &(NEWLINE INDENT)   # Must be followed by indented block
        | TYPE_COMMENT
    
    params:
        | parameters
    
    parameters:
        | slash_no_default param_no_default* param_with_default* [star_etc] 
        | slash_with_default param_with_default* [star_etc] 
        | param_no_default+ param_with_default* [star_etc] 
        | param_with_default+ [star_etc] 
        | star_etc 
    
    # Some duplication here because we can't write (',' | &')'),
    # which is because we don't support empty alternatives (yet).
    #
    slash_no_default:
        | param_no_default+ '/' ',' 
        | param_no_default+ '/' &')' 
    slash_with_default:
        | param_no_default* param_with_default+ '/' ',' 
        | param_no_default* param_with_default+ '/' &')' 
    
    star_etc:
        | '*' param_no_default param_maybe_default* [kwds] 
        | '*' ',' param_maybe_default+ [kwds] 
        | kwds 
    kwds: '**' param_no_default 
    
    # One parameter.  This *includes* a following comma and type comment.
    #
    # There are three styles:
    # - No default
    # - With default
    # - Maybe with default
    #
    # There are two alternative forms of each, to deal with type comments:
    # - Ends in a comma followed by an optional type comment
    # - No comma, optional type comment, must be followed by close paren
    # The latter form is for a final parameter without trailing comma.
    #
    param_no_default:
        | param ',' TYPE_COMMENT? 
        | param TYPE_COMMENT? &')' 
    param_with_default:
        | param default ',' TYPE_COMMENT? 
        | param default TYPE_COMMENT? &')' 
    param_maybe_default:
        | param default? ',' TYPE_COMMENT? 
        | param default? TYPE_COMMENT? &')' 
    param: NAME annotation? 
    
    annotation: ':' expression 
    default: '=' expression 
    
    decorators: ('@' named_expression NEWLINE )+ 
    
    class_def:
        | decorators class_def_raw 
        | class_def_raw
    class_def_raw:
        | 'class' NAME ['(' [arguments] ')' ] ':' block 
    
    block:
        | NEWLINE INDENT statements DEDENT 
        | simple_stmt
    expressions_list: ','.star_expression+ [','] 
    star_expressions:
        | star_expression (',' star_expression )+ [','] 
        | star_expression ',' 
        | star_expression
    star_expression:
        | '*' bitwise_or 
        | expression
    
    star_named_expressions: ','.star_named_expression+ [','] 
    star_named_expression:
        | '*' bitwise_or 
        | named_expression
    named_expression:
        | NAME ':=' ~ expression 
        | expression !':='
    annotated_rhs: yield_expr | star_expressions
    
    expressions:
        | expression (',' expression )+ [','] 
        | expression ',' 
        | expression
    expression:
        | disjunction 'if' disjunction 'else' expression 
        | disjunction
        | lambdef
    
    lambdef:
        | 'lambda' [lambda_params] ':' expression 
    
    lambda_params:
        | lambda_parameters
    
    # lambda_parameters etc. duplicates parameters but without annotations
    # or type comments, and if there's no comma after a parameter, we expect
    # a colon, not a close parenthesis.  (For more, see parameters above.)
    #
    lambda_parameters:
        | lambda_slash_no_default lambda_param_no_default* lambda_param_with_default* [lambda_star_etc] 
        | lambda_slash_with_default lambda_param_with_default* [lambda_star_etc] 
        | lambda_param_no_default+ lambda_param_with_default* [lambda_star_etc] 
        | lambda_param_with_default+ [lambda_star_etc] 
        | lambda_star_etc 
    
    lambda_slash_no_default:
        | lambda_param_no_default+ '/' ',' 
        | lambda_param_no_default+ '/' &':' 
    lambda_slash_with_default:
        | lambda_param_no_default* lambda_param_with_default+ '/' ',' 
        | lambda_param_no_default* lambda_param_with_default+ '/' &':' 
    
    lambda_star_etc:
        | '*' lambda_param_no_default lambda_param_maybe_default* [lambda_kwds] 
        | '*' ',' lambda_param_maybe_default+ [lambda_kwds] 
        | lambda_kwds 
    lambda_kwds: '**' lambda_param_no_default 
    
    lambda_param_no_default:
        | lambda_param ',' 
        | lambda_param &':' 
    lambda_param_with_default:
        | lambda_param default ',' 
        | lambda_param default &':' 
    lambda_param_maybe_default:
        | lambda_param default? ',' 
        | lambda_param default? &':' 
    lambda_param: NAME 
    
    disjunction:
        | conjunction ('or' conjunction )+ 
        | conjunction
    conjunction:
        | inversion ('and' inversion )+ 
        | inversion
    inversion:
        | 'not' inversion 
        | comparison
    comparison:
        | bitwise_or compare_op_bitwise_or_pair+ 
        | bitwise_or
    compare_op_bitwise_or_pair:
        | eq_bitwise_or
        | noteq_bitwise_or
        | lte_bitwise_or
        | lt_bitwise_or
        | gte_bitwise_or
        | gt_bitwise_or
        | notin_bitwise_or
        | in_bitwise_or
        | isnot_bitwise_or
        | is_bitwise_or
    eq_bitwise_or: '==' bitwise_or 
    noteq_bitwise_or:
        | ('!=' ) bitwise_or 
    lte_bitwise_or: '<=' bitwise_or 
    lt_bitwise_or: '<' bitwise_or 
    gte_bitwise_or: '>=' bitwise_or 
    gt_bitwise_or: '>' bitwise_or 
    notin_bitwise_or: 'not' 'in' bitwise_or 
    in_bitwise_or: 'in' bitwise_or 
    isnot_bitwise_or: 'is' 'not' bitwise_or 
    is_bitwise_or: 'is' bitwise_or 
    
    bitwise_or:
        | bitwise_or '|' bitwise_xor 
        | bitwise_xor
    bitwise_xor:
        | bitwise_xor '^' bitwise_and 
        | bitwise_and
    bitwise_and:
        | bitwise_and '&' shift_expr 
        | shift_expr
    shift_expr:
        | shift_expr '<<' sum 
        | shift_expr '>>' sum 
        | sum
    
    sum:
        | sum '+' term 
        | sum '-' term 
        | term
    term:
        | term '*' factor 
        | term '/' factor 
        | term '//' factor 
        | term '%' factor 
        | term '@' factor 
        | factor
    factor:
        | '+' factor 
        | '-' factor 
        | '~' factor 
        | power
    power:
        | await_primary '**' factor 
        | await_primary
    await_primary:
        | AWAIT primary 
        | primary
    primary:
        | invalid_primary  # must be before 'primay genexp' because of invalid_genexp
        | primary '.' NAME 
        | primary genexp 
        | primary '(' [arguments] ')' 
        | primary '[' slices ']' 
        | atom
    
    slices:
        | slice !',' 
        | ','.slice+ [','] 
    slice:
        | [expression] ':' [expression] [':' [expression] ] 
        | expression 
    atom:
        | NAME
        | 'True' 
        | 'False' 
        | 'None' 
        | '__peg_parser__' 
        | strings
        | NUMBER
        | (tuple | group | genexp)
        | (list | listcomp)
        | (dict | set | dictcomp | setcomp)
        | '...' 
    
    strings: STRING+ 
    list:
        | '[' [star_named_expressions] ']' 
    listcomp:
        | '[' named_expression ~ for_if_clauses ']' 
    tuple:
        | '(' [star_named_expression ',' [star_named_expressions]  ] ')' 
    group:
        | '(' (yield_expr | named_expression) ')' 
    genexp:
        | '(' expression ~ for_if_clauses ')' 
    set: '{' expressions_list '}' 
    setcomp:
        | '{' expression ~ for_if_clauses '}' 
    dict:
        | '{' [double_starred_kvpairs] '}' 
    dictcomp:
        | '{' kvpair for_if_clauses '}' 
    double_starred_kvpairs: ','.double_starred_kvpair+ [','] 
    double_starred_kvpair:
        | '**' bitwise_or 
        | kvpair
    kvpair: expression ':' expression 
    for_if_clauses:
        | for_if_clause+
    for_if_clause:
        | ASYNC 'for' star_targets 'in' ~ disjunction ('if' disjunction )* 
        | 'for' star_targets 'in' ~ disjunction ('if' disjunction )* 
    yield_expr:
        | 'yield' 'from' expression 
        | 'yield' [star_expressions] 
    
    arguments:
        | args [','] &')' 
    args:
        | ','.(starred_expression | named_expression !'=')+ [',' kwargs ] 
        | kwargs 
    kwargs:
        | ','.kwarg_or_starred+ ',' ','.kwarg_or_double_starred+ 
        | ','.kwarg_or_starred+
        | ','.kwarg_or_double_starred+
    starred_expression:
        | '*' expression 
    kwarg_or_starred:
        | NAME '=' expression 
        | starred_expression 
    kwarg_or_double_starred:
        | NAME '=' expression 
        | '**' expression 
    # NOTE: star_targets may contain *bitwise_or, targets may not.
    star_targets:
        | star_target !',' 
        | star_target (',' star_target )* [','] 
    star_targets_seq: ','.star_target+ [','] 
    star_target:
        | '*' (!'*' star_target) 
        | t_primary '.' NAME !t_lookahead 
        | t_primary '[' slices ']' !t_lookahead 
        | star_atom
    star_atom:
        | NAME 
        | '(' star_target ')' 
        | '(' [star_targets_seq] ')' 
        | '[' [star_targets_seq] ']' 
    
    single_target:
        | single_subscript_attribute_target
        | NAME 
        | '(' single_target ')' 
    single_subscript_attribute_target:
        | t_primary '.' NAME !t_lookahead 
        | t_primary '[' slices ']' !t_lookahead 
    
    del_targets: ','.del_target+ [','] 
    del_target:
        | t_primary '.' NAME !t_lookahead 
        | t_primary '[' slices ']' !t_lookahead 
        | del_t_atom
    del_t_atom:
        | NAME 
        | '(' del_target ')' 
        | '(' [del_targets] ')' 
        | '[' [del_targets] ']' 
    
    targets: ','.target+ [','] 
    target:
        | t_primary '.' NAME !t_lookahead 
        | t_primary '[' slices ']' !t_lookahead 
        | t_atom
    t_primary:
        | t_primary '.' NAME &t_lookahead 
        | t_primary '[' slices ']' &t_lookahead 
        | t_primary genexp &t_lookahead 
        | t_primary '(' [arguments] ')' &t_lookahead 
        | atom &t_lookahead 
    t_lookahead: '(' | '[' | '.'
    t_atom:
        | NAME 
        | '(' target ')' 
        | '(' [targets] ')' 
        | '[' [targets] ']'

[Grammar_python.gram]: https://github.com/python/cpython/tree/3.9/Grammar/python.gram
[EBNF]: https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form
[PEG]: https://en.wikipedia.org/wiki/Parsing_expression_grammar