10. Full Grammar specification — Python 3.13.2 documentation

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Full Grammar specification</a></li> <li class="right"> <div class="inline-search" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" /> <input type="submit" value="Go" /> </form> </div> | </li> <li class="right"> <label class="theme-selector-label"> Theme <select class="theme-selector" oninput="activateTheme(this.value)"> <option value="auto" selected>Auto</option> <option value="light">Light</option> <option value="dark">Dark</option> </select> </label> |</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <section id="full-grammar-specification"> <h1>10. Full Grammar specification<a class="headerlink" href="#full-grammar-specification" title="Link to this heading">¶</a></h1> This is the full Python grammar, derived directly from the grammar used to generate the CPython parser (see <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/3.13/Grammar/python.gram">Grammar/python.gram</a>). The version here omits details related to code generation and error recovery. The notation is a mixture of <a class="reference external" href="https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form">EBNF</a> and <a class="reference external" href="https://en.wikipedia.org/wiki/Parsing_expression_grammar">PEG</a>. In particular, <code class="docutils literal notranslate">&</code> followed by a symbol, token or parenthesized group indicates a positive lookahead (i.e., is required to match but not consumed), while <code class="docutils literal notranslate">!</code> indicates a negative lookahead (i.e., is required not to match). We use the <code class="docutils literal notranslate">|</code> separator to mean PEG’s “ordered choice” (written as <code class="docutils literal notranslate">/</code> in traditional PEG grammars). See <a class="pep reference external" href="https://peps.python.org/pep-0617/">PEP 617</a> for more details on the grammar’s syntax. <div class="highlight-peg notranslate"><div class="highlight"><pre># 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 ======================= </pre></div> </div> </section> <div class="clearer"></div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="Main"> <div class="sphinxsidebarwrapper"> <div> <h4>Previous topic</h4> <a href="toplevel_components.html" title="previous chapter">9. 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