9. Full Grammar specification
*****************************

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:  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"

   # 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() and input() 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)
   funcdef: 'def' NAME parameters ':' suite
   parameters: '(' [varargslist] ')'
   varargslist: ((fpdef ['=' test] ',')*
                 ('*' NAME [',' '**' NAME] | '**' NAME) |
                 fpdef ['=' test] (',' fpdef ['=' test])* [','])
   fpdef: NAME | '(' fplist ')'
   fplist: fpdef (',' fpdef)* [',']

   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 [',' 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' 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' 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' | ',') 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_comp] ')' |
          '[' [listmaker] ']' |
          '{' [dictorsetmaker] '}' |
          '`' testlist1 '`' |
          NAME | NUMBER | STRING+)
   listmaker: test ( list_for | (',' test)* [','] )
   testlist_comp: 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)* [',']
   dictorsetmaker: ( (test ':' test (comp_for | (',' test ':' test)* [','])) |
                     (test (comp_for | (',' test)* [','])) )

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

   arglist: (argument ',')* (argument [',']
                            |'*' test (',' argument)* [',' '**' test] 
                            |'**' test)
   # 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.
   argument: test [comp_for] | test '=' test

   list_iter: list_for | list_if
   list_for: 'for' exprlist 'in' testlist_safe [list_iter]
   list_if: 'if' old_test [list_iter]

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