Function definition grammar is incorrect

[skirpichev]

cpython/Doc/reference/compound_stmts.rst

Lines 1211 to 1224 in 2f5c3b0

	.. productionlist:: python-grammar
	funcdef: [`decorators`] "def" `funcname` [`type_params`] "(" [`parameter_list`] ")"
	: ["->" `expression`] ":" `suite`
	decorators: `decorator`+
	decorator: "@" `assignment_expression` NEWLINE
	parameter_list: `defparameter` ("," `defparameter`)* "," "/" ["," [`parameter_list_no_posonly`]]
	: | `parameter_list_no_posonly`
	parameter_list_no_posonly: `defparameter` ("," `defparameter`)* ["," [`parameter_list_starargs`]]
	: | `parameter_list_starargs`
	parameter_list_starargs: "*" [`parameter`] ("," `defparameter`)* ["," ["**" `parameter` [","]]]
	: | "**" `parameter` [","]
	parameter: `identifier` [":" `expression`]
	defparameter: `parameter` ["=" `expression`]
	funcname: `identifier`

In parameter_list_starargs - everything can be optional, except for *, and that permits incorrect function definitions like def foo(*):

>>> def foo(*): pass
  File "<stdin>", line 1
    def foo(*): pass
            ^
SyntaxError: named arguments must follow bare *

See d.p.o thread https://discuss.python.org/t/56998. I'll provide a patch, based on suggested solution.

CC @norpadon

Linked PRs

• gh-122845: fix parameter_list_starargs in function definition pseudo-grammar #122847
• [3.13] gh-122845: fix parameter_list_starargs in function definition pseudo-grammar (GH-122847) #129150
• [3.12] gh-122845: fix parameter_list_starargs in function definition pseudo-grammar (GH-122847) #129151

[mashkoor098]

def foo(*args): pass

[skirpichev]

@mashkoor098, not sure I get your point.

def foo(*args):
    pass

is a correct syntax, yes. Another example:

def bar(*, spam='spam!'):
    pass