Validating Specific DataType PYTHON

Question

I am trying to validate the user input to check if it is a string or number.If it is a number I want to say 'Please input letters' This is the code i tried out

while True:
    try:
        member = str(input('Are you a child or adult member? '))
    except TypeError:
        print('Please input letters')

Possible duplicate of How to check if string input is a number? — SalGorithm
– SalGorithm, Commented Mar 25, 2018 at 7:58
Possible duplicate of Data type validation in python - Strings — Mayur
– Mayur, Commented Mar 25, 2018 at 8:00
Digits are just as valid in strings as letters, so there's no way you're going to get a TypeError here. If you want to check the contents of a string, there are lots of methods on the string type that you can see with help(str) in the interactive interpreter or the documentation, including things like isalpha and isdigit. — abarnert
– abarnert, Commented Mar 25, 2018 at 8:03

Joe Iddon · Accepted Answer · 2018-03-25 08:17:46Z

1

In Python3, the input() function always returns a string, even if the string entirely consists of digits, it still returns it as a string, e.g: "123".

So, trying to catch an error when converting it to a string will never work as it is always already a string!

The correct way to do this would be to use .isdigit() to check if it is an integer.

while True:
    member = input('Are you a child or adult member? ');
    if member.isdigit():
        print('Please input letters')
    else:
        break

However, if you want to validate properly, you should not allow the user to enter any string, you should restrict them to "child" or "adult":

while True:
    member = input('Are you a child or adult member? ');
    if member not in ('child', 'adult'):
        print('Please enter a valid entry.')
    else:
        break

answered Mar 25, 2018 at 8:17

Joe Iddon

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