Check Python String Formatting

Question

I can accept user's input in two formats:

1. 123
2. 123,234,6028

I need to write a function/a few lines of code that check whether the input follows the correct format.

The rules:

1. If a single number input, then it should be just a number between 1 and 5 digits long
2. If more then one number, then it should be comma-separated values, but without spaces and letters and no comma/period/letter allowed after the last number.

The function just checks if formatting correct, else it prints Incorrect formatting, try entering again.

I would assume I would need to use re module.

Thanks in advance

Answer 1

You can use a simple regex:

import re

validate = re.compile('\d{1,5}(?:,\d{1,5})*')

validate.fullmatch('123') # valid

validate.fullmatch('123,456,789') # valid

validate.fullmatch('1234567') # invalid

Use in a test:

if validate.fullmatch(your_string):
    # do stuff
else:
    print('Incorrect formatting, try entering again')