Password Validation

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Note: This page contains a small but interesting piece of Python code which I call snippets. You can find more such codes on my Python snippets page.

Contents

  1. Problem
  2. Solution
  3. Explanation

Problem

You're interviewing to join a security team. They want to see you build a password evaluator for your technical interview to validate the input.

Task:
Write a program that takes in a string as input and evaluates it as a valid password. The password is valid if it has at a minimum 2 numbers, 2 of the following special characters ('!', '@', '#', '$', '%', '&', '*'), and a length of at least 7 characters.
If the password passes the check, output 'Strong', else output 'Weak'.

Input Format:
A string representing the password to evaluate.

Output Format:
A string that says 'Strong' if the input meets the requirements, or 'Weak', if not.

Sample Input:
Hello@$World19

Sample Output:
Strong

Solution

Here is my solution to the above problem. Remember that there could be more than one way to solve a problem. If you have a more efficient or concise solution, please leave a comment.

Using RegEx

In [1]:
import re
if re.match('^(?=.*\d.*\d)(?=.*[!@#$%&*].*[!@#$%&*]).{7,}$', input()):
    print("Strong")
else:
    print("Weak")

Strong

Using the conventional method

In [2]:
pw=input()
special_chars=('!', '@', '#', '$', '%', '&', '*')
nums=[str(x) for x in range(10)]
pw_type='Weak'
num_count=0
spcl_count=0
if len(pw)>=7:
    for x in pw:
        if num_count<2 or spcl_count<2:
            if x in nums:
                num_count+=1
            if x in special_chars:
                spcl_count+=1
        else:
            break
    if num_count>=2 and spcl_count>=2:
        pw_type='Strong'
print(pw_type)

Strong

Explanation

As we notice, the RegEx code is comparitively concise and easier to use once you get a hang of it. I will explain only the RegEx code as the conventional code is self explanatory.

My approach (or the algorithm)

Create a RegEx that

  • searches for a number twice.
  • searches for these special characters !@#\$%&* twice.
  • checks if the string length is 7 or above.

The code

  • ^(?=.*\d.*\d)(?=.*[!@#$%&*].*[!@#$%&*]).{7,}$ RegEx pattern
    • ^ matches the beginning of the string.
    • (?=.*\d.*\d) Positive lookahead (searches for at least 2 numbers preceded by any or no characters)
      • . any character.
      • * any number of repetitions of the above including zero. So .* matches any or no characters.
      • \d matches a number (0-9).
    • (?=.*[!@#$%&*].*[!@#$%&*]) Positive lookahead (searches for at least 2 special characters preceded by any or no characters)
      • [!@#$%&*] Character set of special characters given in the problem statement.
    • .{7,} matches any characters occuring 7 times or more in a sequence. Used for measuring password length.
    • $ matches the end of the string.

The problem question is picked from SoloLearn. Here is my SoloLearn code and my SoloLearn profile page.

Last updated 2021-01-09 17:33:06.200287 IST

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