How to check if default value for python function argument is set using inspect?

Question

I'm trying to identify the parameters of a function for which default values are not set. I'm using inspect.signature(func).parameters.value() function which gives a list of function parameters. Since I'm using PyCharm, I can see that the parameters for which the default value is not set have their Parameter.default attribute set to inspect._empty. I'm declaring the function in the following way:

def f(a, b=1):
    pass

So, the default value of a is inspect._empty. Since inspect._empty is a private attribute, I thought that there might be a method for checking if a value is inspect._empty, but I couldn't find it.

Answer 1

You can do it like this:

import inspect


def foo(a, b=1):
    pass


for param in inspect.signature(foo).parameters.values():
    if param.default is param.empty:
        print(param.name)

Output:

a

param.empty holds the same object inspect._empty. I suppose that this way of using it is recommended because of the example in the official documentation of inspect module:

Example: print all keyword-only arguments without default values:

>>>
>>> def foo(a, b, *, c, d=10):
...     pass

>>> sig = signature(foo)
>>> for param in sig.parameters.values():
...     if (param.kind == param.KEYWORD_ONLY and
...                        param.default is param.empty):
...         print('Parameter:', param)
Parameter: c