How to get method parameter names?

python

debugging

introspection

pythonic-way

byAlex Kataev·Feb 18, 2025

To retrieve parameter names from a Python function, use the inspect.signature() method from the inspect module. This returns an ordered mapping of the names directly:

import inspect

def example_method(arg1, arg2):
    pass  # Like a celebrity's autobiography, pretty empty

param_names = list(inspect.signature(example_method).parameters)
print(param_names)  # Outputs: ['arg1', 'arg2'] - still easier than a pop quiz

This piece of code neatly summarizes the parameter names for example_method.

Diving deeper using `inspect`

Sometimes the pool's shallow end isn't enough. For earlier Python versions (prior to 3.3), dive deeper with inspect.getfullargspec():

full_argspec = inspect.getfullargspec(example_method)
print(full_argspec.args)  # Outputs: ['arg1', 'arg2'] - arg3 left for dramatic effect

Here, inspect.getfullargspec() returns an ArgSpec object that opens up more than just argument names such as default values and annotations.

Navigating the maze of dynamic and arbitrary arguments

When functions include *args or **kwargs for handling dynamic arguments, they can still be inspected:

def dynamic_method(*args, **kwargs):
    pass  # pass, the sibling Python never talks about at family reunions

sig = inspect.signature(dynamic_method)
print(sig)  # It's like The Matrix, just *args and **kwargs everywhere

Inspecting such functions is essential for debugging and creating decorators that wrap functions with mysterious signatures.

Python implementation compatibility

Here's a poser: if a function runs fine in CPython, will it glitch when running on a different Python implementation? That's where inspect.signature() comes in handy, as it's the more portable choice:

example_method.__code__.co_varnames  # CPython-specific, use as much as a sorting hat at a muggle school

Advanced signature techniques: A sneak peek

For more sophisticated handling of method parameters, have a look at a popular library like matplotlib. Their source code and documentation offer some great action sequences on keyword argument extraction.

All about introspection and compatibility: The finale

Inspect away: From functions to classes and methods, inspect can reveal a lot about callables.
Interchangeability of function calls: With func(*args, **kwargs), you can pack or unpack positional and keyword arguments at will.
The Pythonic way is the way: Introspection can be powerful, but also brittle. Use it for good, not evil.
Cross-version harmony: To make your code's transition across Python versions smoother, its best to stick with standardized methods.

Introspection: Your debugging sidekick

The power of introspection in Python serves primarily as a debugging tool, allowing developers to diagnose issues effectively, manage errors better, and enhance understanding of functionality.

Additionally, introspection reflects the inherent dynamic nature of Python that enables programs to adapt during runtime based on their own functional behaviors.

Coding guidelines: A Pythonic way

In keeping with Python's philosophy, the use of introspection should be balanced and judicious. While it adds power, it shouldn't lead to unnecessary complexity.

explain-codes / Python / How to get method parameter names?

Linked

What is a Python equivalent of PHP's var_dump()?



Use of *args and **kwargs



How to get the caller's method name in the called method?



How do I access command line arguments?



Getting list of parameter names inside python function

