Python function get *arg name-CodePudding

Given a python function

def func(a, b, *c, **d):
    pass

I can get the names of arguments:

>>> print(func.__code__.co_varnames)
('a', 'b', 'c', 'd')

But how do I know, that c is *args and d is **kwargs??

CodePudding user response：

As far as I know, this information is only accessible via the Signature object returned by inspect.signature. Where that function gets the information, I do not know. (It may be something stored by the implementation that is not otherwise exposed at the Python level.)

>>> import inspect
>>> inspect.signature(func).parameters['a'].kind
<_ParameterKind.POSITIONAL_OR_KEYWORD: 1>
>>> inspect.signature(func).parameters['c'].kind
<_ParameterKind.VAR_POSITIONAL: 2>
>>> inspect.signature(func).parameters['d'].kind
<_ParameterKind.VAR_KEYWORD: 4>

If you look at the definition of _signature_from_function, you'll see it determines the kind by looking at the flags in func.__code__.co_objects and applying some left-to-right logic on the names you see in func.__code__.co_varnames.