How to use Python decorators to check function arg

Question

I would like to define some generic decorators to check arguments before calling some functions.

Something like:

@checkArguments(types = ['int', 'float'])
def myFunction(thisVarIsAnInt, thisVarIsAFloat)
    ''' Here my code '''
    pass

Side notes:

1. Type checking is just here to show an example
2. I'm using Python 2.7 but Python 3.0 whould be interesting too

Answer 1

As you certainly know, it's not pythonic to reject an argument only based on its type.
Pythonic approach is rather "try to deal with it first"
That's why I would rather do a decorator to convert the arguments

def enforce(*types):
    def decorator(f):
        def new_f(*args, **kwds):
            #we need to convert args into something mutable   
            newargs = []        
            for (a, t) in zip(args, types):
               newargs.append( t(a)) #feel free to have more elaborated convertion
            return f(*newargs, **kwds)
        return new_f
    return decorator

This way, your function is fed with the type you expect But if the parameter can quack like a float, it is accepted

@enforce(int, float)
def func(arg1, arg2):
    return arg1 * arg2

print (func(3, 2)) # -> 6.0
print (func('3', 2)) # -> 6.0
print (func('three', 2)) # -> ValueError: invalid literal for int() with base 10: 'three'

I use this trick (with proper conversion method) to deal with vectors.
Many methods I write expect MyVector class as it has plenty of functionalities; but sometime you just want to write

transpose ((2,4))