How Can I Extract Method Parameter Names in Python?

Extracting Method Parameter Names with Python

In Python, determining the names of method parameters can be crucial for refactoring, debugging, or documenting code. Consider a function defined as:

<code class="python">def a_method(arg1, arg2):
    pass</code>

To obtain the names of the parameters as a tuple, there are several approaches:

Using the inspect Module

The inspect module provides an extensive set of functions for examining code objects. It supports extracting parameter names through inspect.getfullargspec():

<code class="python">import inspect
inspect.getfullargspec(a_method)
# Output: (['arg1', 'arg2'], None, None, None)</code>

This returns a tuple containing the names of the positional arguments (in this case, ('arg1', 'arg2')), as well as information about keywords, var-args, and default values (which are not relevant in this example).

Using inspect.signature()

Since Python 3.3, the inspect.signature() function provides a comprehensive view of a callable's signature:

<code class="python">inspect.signature(a_method)
# Output: <Signature (a, b, c=4, *arglist, **keywords)></code>

This reveals the signature with all parameter information, including default values and variable-length arguments.

Caveats

Some callables, particularly built-in functions in CPython, may not be introspectable. Attempting to inspect them may result in a ValueError.

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