10. 完整的语法规范
******************

这是完整的Python语法，它被送入解析器生成器，以生成解析Python源文件的解
析器：

   # 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
