Knowing the signature of a function

[Kent Johnson]

Hello,
pass
How can I query the function object foo to know the number of parameters
it expects. I can find it is a function using callable(f), I can find
some information (listed by dir(foo)) such as the name of the
function,etc.. but nowhere I can find the number of arguments.
I would like to know wether the function expects one or zero arguments.

foo.func_code.co_argcount gives the count of named args. len(foo.func_code.co_varnames) gives the total number of arguments including *args and **kwds args. inspect.getargspec() might also be helpful.

Kent

[Xavier Décoret]

Post by Kent Johnson

Hello,
pass
How can I query the function object foo to know the number of
parameters it expects. I can find it is a function using callable(f),
I can find some information (listed by dir(foo)) such as the name of
the function,etc.. but nowhere I can find the number of arguments.
I would like to know wether the function expects one or zero arguments.

foo.func_code.co_argcount gives the count of named args.
len(foo.func_code.co_varnames) gives the total number of arguments
including *args and **kwds args. inspect.getargspec() might also be
helpful.
Kent

Thanks.

Now I have the following issue: what if foo is not a function but a
callable? inspect.getargspec raises an exception.

I have to do something like:


import inspect

def countargs(f):
if callable(f):
if inspect.isfunction(f): return len(inspect.getargspec(f)[0])
return len(inspect.getargspec(f.__call__)[0])-1
raise ValueError

class foo:
def __call__(self,a,b):
pass

def bar(x):
pass


print countargs(foo)
print countargs(bar)



Is there any better way?

[Steven D'Aprano]

Post by Kent Johnson

How can I query the function object foo to know the number of parameters
it expects. I can find it is a function using callable(f), I can find
some information (listed by dir(foo)) such as the name of the
function,etc.. but nowhere I can find the number of arguments.
I would like to know wether the function expects one or zero arguments.

foo.func_code.co_argcount gives the count of named args.
len(foo.func_code.co_varnames) gives the total number of arguments
including *args and **kwds args. inspect.getargspec() might also be
helpful.

You guys are amazing, have you been spying on me? :-) I was just about to
write in with the same question. Thanks for answering before I asked.

[Xavier Décoret]

Hello,

I have the following code:

def foo(x,y):
pass

How can I query the function object foo to know the number of parameters
it expects. I can find it is a function using callable(f), I can find
some information (listed by dir(foo)) such as the name of the
function,etc.. but nowhere I can find the number of arguments.

I would like to know wether the function expects one or zero arguments.

[Gerald Klix]

... print "tf"
...

Post by Xavier Décoret
import inspect
inspect.getargspec( tf )

(['a', 'b', 'c'], 'arguments', 'keywordArguments', None)

Hello,
pass
How can I query the function object foo to know the number of parameters
it expects. I can find it is a function using callable(f), I can find
some information (listed by dir(foo)) such as the name of the
function,etc.. but nowhere I can find the number of arguments.
I would like to know wether the function expects one or zero arguments.