How to Retrieve Method Parameter Names in Python?

Obtaining Method Parameter Names

Given a defined function like:

def a_method(arg1, arg2):
    pass

How can we retrieve the argument names as a tuple of strings, like ("arg1", "arg2")?

Using the Inspect Module

The inspect module enables us to inspect code objects and retrieve their properties. To obtain the argument names of a_method, use inspect.getfullargspec():

>>> inspect.getfullargspec(a_method)
(['arg1', 'arg2'], None, None, None)

The result consists of the argument names and additional information, such as the names of the args and *kwargs variables and their default values.

def foo(a, b, c=4, *arglist, **keywords): pass
>>> inspect.getfullargspec(foo)
(['a', 'b', 'c'], 'arglist', 'keywords', (4,))

Using inspect.signature()

In Python 3.3 and later, we can use inspect.signature() to obtain the call signature of a callable object:

>>> inspect.signature(foo)
<Signature (a, b, c=4, *arglist, **keywords)>

This provides a more detailed signature, including the parameter types and default values.

Note: Some callables in Python may not be introspectable, especially those defined in C in CPython. In such cases, inspect.getfullargspec() will raise a ValueError.

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