How can I find the number of arguments of a Python function?
import inspect
inspect.getargspec(someMethod)
see the inspect module
The previously accepted answer has been deprecated as of Python 3.0
. Instead of using inspect.getargspec
you should now opt for the Signature
class which superseded it.
Creating a Signature for the function is easy via the signature
function:
from inspect import signature
def someMethod(self, arg1, kwarg1=None):
pass
sig = signature(someMethod)
Now, you can either view its parameters quickly by str
ing it:
str(sig) # returns: '(self, arg1, kwarg1=None)'
or you can also get a mapping of attribute names to parameter objects via sig.parameters
.
params = sig.parameters
print(params['kwarg1']) # prints: kwarg1=20
Additionally, you can call len
on sig.parameters
to also see the number of arguments this function requires:
print(len(params)) # 3
Each entry in the params
mapping is actually a Parameter
object that has further attributes making your life easier. For example, grabbing a parameter and viewing its default value is now easily performed with:
kwarg1 = params['kwarg1']
kwarg1.default # returns: None
similarly for the rest of the objects contained in parameters
.
As for Python 2.x
users, while inspect.getargspec
isn't deprecated, the language will soon be :-). The Signature
class isn't available in the 2.x
series and won't be. So you still need to work with inspect.getargspec
.
As for transitioning between Python 2 and 3, if you have code that relies on the interface of getargspec
in Python 2 and switching to signature
in 3
is too difficult, you do have the valuable option of using inspect.getfullargspec
. It offers a similar interface to getargspec
(a single callable argument) in order to grab the arguments of a function while also handling some additional cases that getargspec
doesn't:
from inspect import getfullargspec
def someMethod(self, arg1, kwarg1=None):
pass
args = getfullargspec(someMethod)
As with getargspec
, getfullargspec
returns a NamedTuple
which contains the arguments.
print(args)
FullArgSpec(args=['self', 'arg1', 'kwarg1'], varargs=None, varkw=None, defaults=(None,), kwonlyargs=[], kwonlydefaults=None, annotations={})