Newbie Help

[cronje_med]

Ok, so I'm a bit new at this, so please don't make fun of me too much.

I was trying to make a math function that wouldn't pull a NameError 
if I didn't enter a number or variable containing a number. Here's 
what I have:

def math(num):
        if num.isdigit() == 1:
            print "Is a number!"
            return num
        else:
            print "Is not a number!"
            return num

>>> math(5+5)
AttributeError: 'int' object has no attribute 'isdigit'
>>> math("5+5")
Is not a number!
'5+5'
>>> math("5+x")
Is not a number!
'5+x'

Any help anyone can provide would be great. Thank you.