Prompt
The most obvious bad practice here is the use of a global variable. Instead of setting num as a side-effect, your function should return the result.
getNum() is not such a good name for the function. PEP 8, the official style guide for Python, says that function names should be lower_case_with_underscores. Furthermore, "get" implies that the function is retrieving a piece of data that is already stored somewhere, which is not the case here. Finally, "Num" should be more specific.
The use of recursion is not appropriate. If you want a loop, write a loop.
def ask_integer():""" Return an integer entered by the user (repeatedly prompting if the input is not a valid integer).""" while True: try: return int(input("> ")) except ValueError: print("Please enter an integer")num = ask_integer()collatz function
Strictly speaking, you didn't follow the instructions. Your solution isn't wrong or bad — you just didn't implement the collatz function according to the specification that was given, which says that you should print and return one single number.
def collatz(num):""" Given a number, print and return its successor in the Collatz sequence.""" next = num // 2 if num % 2 == 0 else 3 * num + 1 print(next) return nextnum = ask_integer()while num > 1: num = collatz(num)