Python list function argument names

Question

Is there a way to get the parameter names a function takes?

def foo(bar, buz):
    pass

magical_way(foo) == ["bar", "buz"]

Solution 1

Use the inspect module from Python's standard library (the cleanest, most solid way to perform introspection).

Specifically, inspect.getargspec(f) returns the names and default values of f's arguments -- if you only want the names and don't care about special forms *a, **k,

import inspect

def magical_way(f):
    return inspect.getargspec(f)[0]

completely meets your expressed requirements.

Solution 2

>>> import inspect
>>> def foo(bar, buz):
...     pass
... 
>>> inspect.getargspec(foo)
ArgSpec(args=['bar', 'buz'], varargs=None, keywords=None, defaults=None)
>>> def magical_way(func):
...     return inspect.getargspec(func).args
... 
>>> magical_way(foo)
['bar', 'buz']

Comments

[Sasha Chedygov]

Duplicate: stackoverflow.com/questions/582056/…, stackoverflow.com/questions/218616/…

[Bemmu]

Maybe one more is warranted, since I spent a good half an hour trying to Google this without hitting those dupes.

[episodeyang]

This is the first hit on Google now, thanks to the way OP asked the question. Making answers easier to find by framing the question better is definitely relevant to UX of those looking for answers.

[Bemmu]

Btw. I have since learned that it's wrong to say "argument" here, as receiving variables are parameters, not arguments.

[John La Rooy]

you can also use return inspect.getargspec(f).args

[Wolph]

Note that .args only works in Python 2.6 and up. For older verions you have to use [0] instead.

[Alex Martelli]

@gnibbler, true, in Python 2.6 or better only (so not if you're using Python with App Engine (or apps embedding Python 2.5 or earlier); I gave the approach that works in any Python (since 2.1 when inspect was added to the standard library).

[Chinmay Kanchi]

+1 for providing the magical_way() function.

[Luke Murray]

maybe you can edit this since getargspec is now deprecated and inspect.signature() is favored instead

[juan Isaza]

inspect.getargspec is deprecated as of Python 3.6. Instead one should use inspect.signature. Any one knows how to use it?, thanks

[lovesh]

@juanIsaza inspect.signature(f).parameters

[Dasmowenator]

You can also inspect a constructor's arguments using "inspect.getargspec(MyClass.__init__)[0]" as mentioned here: stackoverflow.com/a/36849919/367544

[TheGrimmScientist]

that function name tho

[Mauricio Arboleda]

@juanIsaza alternative you can use inspect.getfullargspec(f).args or inspect.getfullargspec(f)[0] (python 3.7)