Should I force Python type checking?

Question

Perhaps as a remnant of my days with a strongly-typed language (Java), I often find myself writing functions and then forcing type checks. For example:

def o         


        

Answer 1

Two things.

First, if you're willing to spend ~$200, you can get a pretty good python IDE. I use PyCharm and have been really impressed. (It's by the same people who make ReSharper for C#.) It will analyze your code as you write it, and look for places where variables are of the wrong type (among a pile of other things).

Second:

Before I used PyCharm, I ran in to the same problem--namely, I'd forget about the specific signatures of functions I wrote. I may have found this somewhere, but maybe I wrote it (I can't remember now). But anyway it's a decorator that you can use around your function definitions that does the type checking for you.

Call it like this

@require_type('paramA', str)
@require_type('paramB', list)
@require_type('paramC', collections.Counter)
def my_func(paramA, paramB, paramC):
    paramB.append(paramC[paramA].most_common())
    return paramB

Anyway, here's the code of the decorator.

def require_type(my_arg, *valid_types):
    '''
        A simple decorator that performs type checking.

        @param my_arg: string indicating argument name
        @param valid_types: *list of valid types
    '''
    def make_wrapper(func):
        if hasattr(func, 'wrapped_args'):
            wrapped = getattr(func, 'wrapped_args')
        else:
            body = func.func_code
            wrapped = list(body.co_varnames[:body.co_argcount])

        try:
            idx = wrapped.index(my_arg)
        except ValueError:
            raise(NameError, my_arg)

        def wrapper(*args, **kwargs):

            def fail():
                all_types = ', '.join(str(typ) for typ in valid_types)
                raise(TypeError, '\'%s\' was type %s, expected to be in following list: %s' % (my_arg, all_types, type(arg)))

            if len(args) > idx:
                arg = args[idx]
                if not isinstance(arg, valid_types):
                    fail()
            else:
                if my_arg in kwargs:
                    arg = kwargs[my_arg]
                    if not isinstance(arg, valid_types):
                        fail()

            return func(*args, **kwargs)

        wrapper.wrapped_args = wrapped
        return wrapper
    return make_wrapper