1, 2, Fizz, 4, Buzz: FizzBuzz
getString and maxNum should be get_string and max_num, by PEP 8 recommendation.
getString sometimes returns a number, and sometimes returns a string.  This violates the expectation set up by the function name.  Also, a function that is indecisive about its return type is harder to work with.
num = 1; ← No semicolons in Python, please.
The fizzbuzz loop is written idiomatically as for num in range(1, maxNum + 1): …