Forcing integer input using the isdigit() method

Question

Is the following code conventionally acceptable and what are some problems that may arise from implementing the required solution in such a manner?

while True:
    Iq = input("What is your Iq? ")
    if Iq.isdigit():
        print(Iq)
        break
    else:
        print("that is not a number")

Answer 1

Potential problems with using .isdigit() to validate numeric input are:

• It doesn't handle negative numbers. Sometimes, this is expected behavior. I doubt that any of your users would actually have a negative IQ. However, for questions like “What's the current temperature?” (in winter) or “What's the current balance of your bank account?” (if it's overdrawn), negative numbers could be legal inputs.
• It doesn't handle floating-point numbers. Again, this could be a desired feature in cases where only whole-number inputs make sense.

Even if you do want to restrict the user to entering positive whole numbers, you might want to have different error messages for negative/non-integer inputs than for completely non-numeric inputs such as abc or the empty string.

Here's a more robust input function, which allows negative or non-integer inputs, and also supports optional bounds-checking for the value.

def input_int(prompt='', lo_value=None, hi_value=None):
    while True:
        # Have the user input a string.
        entry = input(prompt)
        # Try to parse the string as a number.
        try:
            value = int(entry)
        except ValueError:
            # If they entered a float, round it to an int.
            try:
                value = round(float(entry))
            except ValueError:
                print('That is not a number.')
                continue
        # Bounds check the value.
        if (lo_value is not None) and (value < lo_value):
            print(f'Value cannot be less than {lo_value}.')
        elif (hi_value is not None) and (value > hi_value):
            print(f'Value cannot be more than {hi_value}.')
        else:
            return value