Programmatically determining amount of parameters a function requires - Python [duplicate]

Question

I was creating a simple command line utility and using a dictionary as a sort of case statement with key words linking to their appropriate function. The functions all have different amount of arguments required so currently to check if the user entered the correct amount of arguments needed for each function I placed the required amount inside the dictionary case statement in the form {Keyword:(FunctionName, AmountofArguments)}.

This current setup works perfectly fine however I was just wondering in the interest of self improval if there was a way to determine the required number of arguments in a function and my google attempts have returned so far nothing of value but I see how args and kwargs could screw such a command up because of the limitless amount of arguments they allow.

Answer 1

inspect.getargspec():

Get the names and default values of a function’s arguments. A tuple of four things is returned: (args, varargs, varkw, defaults). args is a list of the argument names (it may contain nested lists). varargs and varkw are the names of the * and ** arguments or None. defaults is a tuple of default argument values or None if there are no default arguments; if this tuple has n elements, they correspond to the last n elements listed in args.

Answer 2

What you want is in general not possible, because of the use of varargs and kwargs, but inspect.getargspec (Python 2.x) and inspect.getfullargspec (Python 3.x) come close.

• Python 2.x:

  >>> import inspect >>> def add(a, b=0): ...     return a + b ... >>> inspect.getargspec(add) (['a', 'b'], None, None, (0,)) >>> len(inspect.getargspec(add)[0]) 2 

• Python 3.x:

  >>> import inspect >>> def add(a, b=0): ...     return a + b ... >>> inspect.getfullargspec(add) FullArgSpec(args=['a', 'b'], varargs=None, varkw=None, defaults=(0,), kwonlyargs=[], kwonlydefaults=None, annotations={}) >>> len(inspect.getfullargspec(add).args) 2