How to see if a string only contains certain characters, and if they do, return True, else return False: Python

For python 3.4.1, how would you go about finding if certain characters are in your string? I tried doing it this way:

def isItBinary(myString):
    for ele in myString:
        if ele == '1' or if ele == '0':
            return True
        else:
            return False

The problem with this code is that if I type isItBinary('102'), it will return True. I just want it to return True if and only if it contains '1' or '0'.