Validation in Python

Problem Statement:

We are given a string, we need to check whether the string is a valid username or not. To be a valid username, the string should satisfy the following conditions:

  • The string should only contain letters, numbers, or underscore(s).
  • It should not start with a number.
  • It should not end with an underscore.
  • Its length should be greater than equal to 4 and less than equal to 25.

Code for Validation in Python:

def check_username(s):
    alphabets = list('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
    numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
    if (type(s[0]) != str):
        return 'Invalid Username1'
    if (len(s)<4):
        return 'Invalid Username2'
    if (len(s)>25):
        return 'Invalid Username3'
    if (s[-1] == '_'):
        return 'Invalid Username4'
    for i in s:
        if (i in alphabets) or (i == '_') or (i in numbers):
        return 'Invalid Username5'
    return 'Valid Username'

t = int(input('Enter number of test cases: '))
for i in range(t):
    s = input('\nEnter username: ')
    s = list(s)
    for i in range(len(s)):
            s[i] = int(s[i])
    print(check_username(s), '\n')


Output for Validation in Python

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