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Password validation in Python

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Let’s take a password as a combination of alphanumeric characters along with special characters, and check whether the password is valid or not with the help of few conditions. Conditions for a valid password are:

  1. Should have at least one number.
  2. Should have at least one uppercase and one lowercase character.
  3. Should have at least one special symbol.
  4. Should be between 6 to 20 characters long.
Input :  Geek12#
Output : Password is valid.

Input :  asd123
Output : Invalid Password !!

We can check if a given string is eligible to be a password or not using multiple ways. Method #1: Naive Method (Without using Regex). 

Python3

# Password validation in Python
# using naive method
 
# Function to validate the password
def password_check(passwd):
     
    SpecialSym =['$', '@', '#', '%']
    val = True
     
    if len(passwd) < 6:
        print('length should be at least 6')
        val = False
         
    if len(passwd) > 20:
        print('length should be not be greater than 8')
        val = False
         
    if not any(char.isdigit() for char in passwd):
        print('Password should have at least one numeral')
        val = False
         
    if not any(char.isupper() for char in passwd):
        print('Password should have at least one uppercase letter')
        val = False
         
    if not any(char.islower() for char in passwd):
        print('Password should have at least one lowercase letter')
        val = False
         
    if not any(char in SpecialSym for char in passwd):
        print('Password should have at least one of the symbols $@#')
        val = False
    if val:
        return val
 
# Main method
def main():
    passwd = 'Geek12@'
     
    if (password_check(passwd)):
        print("Password is valid")
    else:
        print("Invalid Password !!")
         
# Driver Code       
if __name__ == '__main__':
    main()

                    
Output:
Password is valid

This code used boolean functions to check if all the conditions were satisfied or not. We see that though the complexity of the code is basic, the length is considerable.   Method #2: Using regex compile() method of Regex module makes a Regex object, making it possible to execute regex functions onto the pat variable. Then we check if the pattern defined by pat is followed by the input string passwd. If so, the search method returns true, which would allow the password to be valid. 

Python3

# importing re library
import re
 
def main():
    passwd = 'Geek12@'
    reg = "^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*#?&])[A-Za-z\d@$!#%*?&]{6,20}$"
     
    # compiling regex
    pat = re.compile(reg)
     
    # searching regex                
    mat = re.search(pat, passwd)
     
    # validating conditions
    if mat:
        print("Password is valid.")
    else:
        print("Password invalid !!")
 
# Driver Code    
if __name__ == '__main__':
    main()

                    
Output:
Password is valid.

Using ascii values and for loop:

This code uses a function that checks if a given password satisfies certain conditions. It uses a single for loop to iterate through the characters in the password string, and checks if the password contains at least one digit, one uppercase letter, one lowercase letter, and one special symbol from a predefined list and based on ascii values. It sets a boolean variable “val” to True if all these conditions are satisfied, and returns “val” at the end of the function.

The time complexity of this code is O(n), where n is the length of the password string. The space complexity is O(1), as the size of the variables used in the function does not depend on the size of the input.

Python3

def password_check(passwd):
    SpecialSym =['$', '@', '#', '%']
    val = True
    if len(passwd) < 6:
        print('length should be at least 6')
        val = False
    if len(passwd) > 20:
        print('length should be not be greater than 8')
        val = False
 
    # Check if password contains at least one digit, uppercase letter, lowercase letter, and special symbol
    has_digit = False
    has_upper = False
    has_lower = False
    has_sym = False
    for char in passwd:
        if ord(char) >= 48 and ord(char) <= 57:
            has_digit = True
        elif ord(char) >= 65 and ord(char) <= 90:
            has_upper = True
        elif ord(char) >= 97 and ord(char) <= 122:
            has_lower = True
        elif char in SpecialSym:
            has_sym = True
 
    if not has_digit:
        print('Password should have at least one numeral')
        val = False
    if not has_upper:
        print('Password should have at least one uppercase letter')
        val = False
    if not has_lower:
        print('Password should have at least one lowercase letter')
        val = False
    if not has_sym:
        print('Password should have at least one of the symbols $@#')
        val = False
 
    return val
print(password_check('Geek12@')) # should return True
print(password_check('asd123')) # should return False
print(password_check('HELLOworld')) # should return False
print(password_check('helloWORLD123@')) # should return True
print(password_check('HelloWORLD123')) # should return False
#This code is contributed by Edula Vinay Kumar Reddy

                    

Output
True
Password should have at least one uppercase letter
Password should have at least one of the symbols $@#
False
Password should have at least one numeral
Password should have at least one of the symbols $@#
False
True
Password should have at least one of the symbols $@#
False


Last Updated : 30 Dec, 2022
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