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"]

Duplicate: http://stackoverflow.com/questions/582056/getting-list-of-parameters-inside-python-function, http://stackoverflow.com/questions/218616/getting-method-parameter-names-in-python — Sasha Chedygov, Aug 19 '10 at 01:25
Maybe one more is warranted, since I spent a good half an hour trying to Google this without hitting those dupes. — Bemmu, Aug 19 '10 at 02:03
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. — episodeyang, Apr 13 '17 at 19:44
Btw. I have since learned that it's wrong to say "argument" here, as receiving variables are **parameters**, not arguments. — Bemmu, May 31 '19 at 05:47

score 75 · Accepted Answer · edited Jan 23 '19 at 04:36

75

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.

edited Jan 23 '19 at 04:36

Nathaniel Jones

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answered Aug 19 '10 at 00:45

Alex Martelli

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you can also use `return inspect.getargspec(f).args` – John La Rooy Aug 19 '10 at 00:56
@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). – Alex Martelli Aug 19 '10 at 01:05
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maybe you can edit this since getargspec is now deprecated and inspect.signature() is favored instead – Luke Murray Dec 14 '16 at 15:21
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inspect.getargspec is deprecated as of Python 3.6. Instead one should use inspect.signature. Any one knows how to use it?, thanks – juan Isaza Apr 12 '17 at 02:54
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@juanIsaza `inspect.signature(f).parameters` – lovesh May 30 '17 at 11:50
You can also inspect a constructor's arguments using "inspect.getargspec(MyClass.__init__)[0]" as mentioned here: https://stackoverflow.com/a/36849919/367544 – Dasmowenator Mar 27 '18 at 18:36
that function name tho – TheGrimmScientist Aug 01 '19 at 18:47
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@juanIsaza alternative you can use inspect.getfullargspec(f).args or inspect.getfullargspec(f)[0] (python 3.7) – Mauricio Arboleda-Zapata Nov 19 '20 at 07:25

John La Rooy · Answer 2 · 2010-08-19T00:57:31.720

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>>> 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']

edited Aug 19 '10 at 00:57

answered Aug 19 '10 at 00:49

John La Rooy

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Note that `.args` only works in Python 2.6 and up. For older verions you have to use `[0]` instead. – Wolph Aug 19 '10 at 01:03
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+1 for providing the `magical_way()` function. – Chinmay Kanchi Aug 19 '10 at 01:22

Python list function argument names

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