10. 完整的语法规范

10. 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)。 这里显示的版本省略了有关代码生成和错误恢复的细节。

该标记法是 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肯定型前视（即要求匹配但不消耗字符）。而 ! 表示否定型前视（即要求 不 匹配）。 我们使用 | 分隔符来表示 PEG 的“有序选择”（在传统 PEG 语法中为 / 写法）。 请参阅 PEP 617 了解有关该语法规则的更多细节。

## PEG grammar for Python

## ========================= START OF THE GRAMMAR =========================

## General grammatical elements and rules:
#
## * Strings with double quotes (") denote SOFT KEYWORDS
## * Strings with single quotes (') denote KEYWORDS
## * Upper case names (NAME) denote tokens in the Grammar/Tokens file
## * Rule names starting with "invalid_" are used for specialized syntax errors
##     - These rules are NOT used in the first pass of the parser.
##     - Only if the first pass fails to parse, a second pass including the invalid
##       rules will be executed.
##     - If the parser fails in the second phase with a generic syntax error, the
##       location of the generic failure of the first pass will be used (this avoids
##       reporting incorrect locations due to the invalid rules).
##     - The order of the alternatives involving invalid rules matter
##       (like any rule in PEG).
#
## Grammar Syntax (see PEP 617 for more information):
#
## rule_name: expression
##   Optionally, a type can be included right after the rule name, which
##   specifies the return type of the C or Python function corresponding to the
##   rule:
## rule_name[return_type]: expression
##   If the return type is omitted, then a void * is returned in C and an Any in
##   Python.
## e1 e2
##   Match e1, then match e2.
## e1 | e2
##   Match e1 or e2.
##   The first alternative can also appear on the line after the rule name for
##   formatting purposes. In that case, a | must be used before the first
##   alternative, like so:
##       rule_name[return_type]:
##            | first_alt
##            | second_alt
## ( e )
##   Match e (allows also to use other operators in the group like '(e)*')
## [ e ] or e?
##   Optionally match e.
## e*
##   Match zero or more occurrences of e.
## e+
##   Match one or more occurrences of e.
## s.e+
##   Match one or more occurrences of e, separated by s. The generated parse tree
##   does not include the separator. This is otherwise identical to (e (s e)*).
## &e
##   Succeed if e can be parsed, without consuming any input.
## !e
##   Fail if e can be parsed, without consuming any input.
## ~
##   Commit to the current alternative, even if it fails to parse.
## &&e
##   Eager parse e. The parser will not backtrack and will immediately
##   fail with SyntaxError if e cannot be parsed.
#

## STARTING RULES
## ==============

file: [statements] ENDMARKER
interactive: statement_newline
eval: expressions NEWLINE* ENDMARKER
func_type: '(' [type_expressions] ')' '->' expression NEWLINE* ENDMARKER

## GENERAL STATEMENTS
## ==================

statements: statement+

statement: compound_stmt  | simple_stmts

statement_newline:
    | compound_stmt NEWLINE
    | simple_stmts
    | NEWLINE
    | ENDMARKER

simple_stmts:
    | simple_stmt !';' NEWLINE  # Not needed, there for speedup
    | ';'.simple_stmt+ [';'] NEWLINE

## NOTE: assignment MUST precede expression, else parsing a simple assignment
## will throw a SyntaxError.
simple_stmt:
    | assignment
    | type_alias
    | 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
    | match_stmt

## SIMPLE STATEMENTS
## =================

## 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)

annotated_rhs: yield_expr | star_expressions

augassign:
    | '+='
    | '-='
    | '*='
    | '@='
    | '/='
    | '%='
    | '&='
    | '|='
    | '^='
    | '<<='
    | '>>='
    | '**='
    | '//='

return_stmt:
    | 'return' [star_expressions]

raise_stmt:
    | 'raise' expression ['from' expression ]
    | 'raise'

global_stmt: 'global' ','.NAME+

nonlocal_stmt: 'nonlocal' ','.NAME+

del_stmt:
    | 'del' del_targets &(';' | NEWLINE)

yield_stmt: yield_expr

assert_stmt: 'assert' expression [',' expression ]

import_stmt:
    | import_name
    | import_from

## Import statements
## -----------------

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

## COMPOUND STATEMENTS
## ===================

## Common elements
## ---------------

block:
    | NEWLINE INDENT statements DEDENT
    | simple_stmts

decorators: ('@' named_expression NEWLINE )+

## Class definitions
## -----------------

class_def:
    | decorators class_def_raw
    | class_def_raw

class_def_raw:
    | 'class' NAME [type_params] ['(' [arguments] ')' ] ':' block

## Function definitions
## --------------------

function_def:
    | decorators function_def_raw
    | function_def_raw

function_def_raw:
    | 'def' NAME [type_params] '(' [params] ')' ['->' expression ] ':' [func_type_comment] block
    | 'async' 'def' NAME [type_params] '(' [params] ')' ['->' expression ] ':' [func_type_comment] block

## Function parameters
## -------------------

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_no_default_star_annotation 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_no_default_star_annotation:
    | param_star_annotation ',' TYPE_COMMENT?
    | param_star_annotation 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?
param_star_annotation: NAME star_annotation
annotation: ':' expression
star_annotation: ':' star_expression
default: '=' expression  | invalid_default

## If statement
## ------------

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 statement
## ---------------

while_stmt:
    | 'while' named_expression ':' block [else_block]

## For statement
## -------------

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 statement
## --------------

with_stmt:
    | 'with' '(' ','.with_item+ ','? ')' ':' [TYPE_COMMENT] 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 statement
## -------------

try_stmt:
    | 'try' ':' block finally_block
    | 'try' ':' block except_block+ [else_block] [finally_block]
    | 'try' ':' block except_star_block+ [else_block] [finally_block]

## Except statement
## ----------------

except_block:
    | 'except' expression ['as' NAME ] ':' block
    | 'except' ':' block
except_star_block:
    | 'except' '*' expression ['as' NAME ] ':' block
finally_block:
    | 'finally' ':' block

## Match statement
## ---------------

match_stmt:
    | "match" subject_expr ':' NEWLINE INDENT case_block+ DEDENT

subject_expr:
    | star_named_expression ',' star_named_expressions?
    | named_expression

case_block:
    | "case" patterns guard? ':' block

guard: 'if' named_expression

patterns:
    | open_sequence_pattern
    | pattern

pattern:
    | as_pattern
    | or_pattern

as_pattern:
    | or_pattern 'as' pattern_capture_target

or_pattern:
    | '|'.closed_pattern+

closed_pattern:
    | literal_pattern
    | capture_pattern
    | wildcard_pattern
    | value_pattern
    | group_pattern
    | sequence_pattern
    | mapping_pattern
    | class_pattern

## Literal patterns are used for equality and identity constraints
literal_pattern:
    | signed_number !('+' | '-')
    | complex_number
    | strings
    | 'None'
    | 'True'
    | 'False'

## Literal expressions are used to restrict permitted mapping pattern keys
literal_expr:
    | signed_number !('+' | '-')
    | complex_number
    | strings
    | 'None'
    | 'True'
    | 'False'

complex_number:
    | signed_real_number '+' imaginary_number
    | signed_real_number '-' imaginary_number

signed_number:
    | NUMBER
    | '-' NUMBER

signed_real_number:
    | real_number
    | '-' real_number

real_number:
    | NUMBER

imaginary_number:
    | NUMBER

capture_pattern:
    | pattern_capture_target

pattern_capture_target:
    | !"_" NAME !('.' | '(' | '=')

wildcard_pattern:
    | "_"

value_pattern:
    | attr !('.' | '(' | '=')

attr:
    | name_or_attr '.' NAME

name_or_attr:
    | attr
    | NAME

group_pattern:
    | '(' pattern ')'

sequence_pattern:
    | '[' maybe_sequence_pattern? ']'
    | '(' open_sequence_pattern? ')'

open_sequence_pattern:
    | maybe_star_pattern ',' maybe_sequence_pattern?

maybe_sequence_pattern:
    | ','.maybe_star_pattern+ ','?

maybe_star_pattern:
    | star_pattern
    | pattern

star_pattern:
    | '*' pattern_capture_target
    | '*' wildcard_pattern

mapping_pattern:
    | '{' '}'
    | '{' double_star_pattern ','? '}'
    | '{' items_pattern ',' double_star_pattern ','? '}'
    | '{' items_pattern ','? '}'

items_pattern:
    | ','.key_value_pattern+

key_value_pattern:
    | (literal_expr | attr) ':' pattern

double_star_pattern:
    | '**' pattern_capture_target

class_pattern:
    | name_or_attr '(' ')'
    | name_or_attr '(' positional_patterns ','? ')'
    | name_or_attr '(' keyword_patterns ','? ')'
    | name_or_attr '(' positional_patterns ',' keyword_patterns ','? ')'

positional_patterns:
    | ','.pattern+

keyword_patterns:
    | ','.keyword_pattern+

keyword_pattern:
    | NAME '=' pattern

## Type statement
## ---------------

type_alias:
    | "type" NAME [type_params] '=' expression

## Type parameter declaration
## --------------------------

type_params:
    | invalid_type_params
    | '[' type_param_seq ']'

type_param_seq: ','.type_param+ [',']

type_param:
    | NAME [type_param_bound] [type_param_default]
    | '*' NAME [type_param_starred_default]
    | '**' NAME [type_param_default]

type_param_bound: ':' expression
type_param_default: '=' expression
type_param_starred_default: '=' star_expression

## EXPRESSIONS
## -----------

expressions:
    | expression (',' expression )+ [',']
    | expression ','
    | expression

expression:
    | disjunction 'if' disjunction 'else' expression
    | disjunction
    | lambdef

yield_expr:
    | 'yield' 'from' expression
    | 'yield' [star_expressions]

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

assignment_expression:
    | NAME ':=' ~ expression

named_expression:
    | assignment_expression
    | expression !':='

disjunction:
    | conjunction ('or' conjunction )+
    | conjunction

conjunction:
    | inversion ('and' inversion )+
    | inversion

inversion:
    | 'not' inversion
    | comparison

## Comparison operators
## --------------------

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 operators
## -----------------

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

## Arithmetic operators
## --------------------

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

## Primary elements
## ----------------

## Primary elements are things like "obj.something.something", "obj[something]", "obj(something)", "obj" ...

await_primary:
    | 'await' primary
    | primary

primary:
    | primary '.' NAME
    | primary genexp
    | primary '(' [arguments] ')'
    | primary '[' slices ']'
    | atom

slices:
    | slice !','
    | ','.(slice | starred_expression)+ [',']

slice:
    | [expression] ':' [expression] [':' [expression] ]
    | named_expression

atom:
    | NAME
    | 'True'
    | 'False'
    | 'None'
    | strings
    | NUMBER
    | (tuple | group | genexp)
    | (list | listcomp)
    | (dict | set | dictcomp | setcomp)
    | '...'

group:
    | '(' (yield_expr | named_expression) ')'

## Lambda functions
## ----------------

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

## LITERALS
## ========

fstring_middle:
    | fstring_replacement_field
    | FSTRING_MIDDLE
fstring_replacement_field:
    | '{' annotated_rhs '='? [fstring_conversion] [fstring_full_format_spec] '}'
fstring_conversion:
    | "!" NAME
fstring_full_format_spec:
    | ':' fstring_format_spec*
fstring_format_spec:
    | FSTRING_MIDDLE
    | fstring_replacement_field
fstring:
    | FSTRING_START fstring_middle* FSTRING_END

string: STRING
strings: (fstring|string)+

list:
    | '[' [star_named_expressions] ']'

tuple:
    | '(' [star_named_expression ',' [star_named_expressions]  ] ')'

set: '{' star_named_expressions '}'

## Dicts
## -----

dict:
    | '{' [double_starred_kvpairs] '}'

double_starred_kvpairs: ','.double_starred_kvpair+ [',']

double_starred_kvpair:
    | '**' bitwise_or
    | kvpair

kvpair: expression ':' expression

## Comprehensions & Generators
## ---------------------------

for_if_clauses:
    | for_if_clause+

for_if_clause:
    | 'async' 'for' star_targets 'in' ~ disjunction ('if' disjunction )*
    | 'for' star_targets 'in' ~ disjunction ('if' disjunction )*

listcomp:
    | '[' named_expression for_if_clauses ']'

setcomp:
    | '{' named_expression for_if_clauses '}'

genexp:
    | '(' ( assignment_expression | expression !':=') for_if_clauses ')'

dictcomp:
    | '{' kvpair for_if_clauses '}'

## FUNCTION CALL ARGUMENTS
## =======================

arguments:
    | args [','] &')'

args:
    | ','.(starred_expression | ( assignment_expression | 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

## ASSIGNMENT TARGETS
## ==================

## Generic targets
## ---------------

## NOTE: star_targets may contain *bitwise_or, targets may not.
star_targets:
    | star_target !','
    | star_target (',' star_target )* [',']

star_targets_list_seq: ','.star_target+ [',']

star_targets_tuple_seq:
    | star_target (',' star_target )+ [',']
    | star_target ','

star_target:
    | '*' (!'*' star_target)
    | target_with_star_atom

target_with_star_atom:
    | t_primary '.' NAME !t_lookahead
    | t_primary '[' slices ']' !t_lookahead
    | star_atom

star_atom:
    | NAME
    | '(' target_with_star_atom ')'
    | '(' [star_targets_tuple_seq] ')'
    | '[' [star_targets_list_seq] ']'

single_target:
    | single_subscript_attribute_target
    | NAME
    | '(' single_target ')'

single_subscript_attribute_target:
    | t_primary '.' NAME !t_lookahead
    | t_primary '[' slices ']' !t_lookahead

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: '(' | '[' | '.'

## Targets for del statements
## --------------------------

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] ']'

## TYPING ELEMENTS
## ---------------

## type_expressions allow */** but ignore them
type_expressions:
    | ','.expression+ ',' '*' expression ',' '**' expression
    | ','.expression+ ',' '*' expression
    | ','.expression+ ',' '**' expression
    | '*' expression ',' '**' expression
    | '*' expression
    | '**' expression
    | ','.expression+

func_type_comment:
    | NEWLINE TYPE_COMMENT &(NEWLINE INDENT)   # Must be followed by indented block
    | TYPE_COMMENT

## ========================= END OF THE GRAMMAR ===========================

## ========================= START OF INVALID RULES =======================