Python program to check the validity of a Password

In this program, we will be taking a password as a combination of alphanumeric characters along with special characters, and checking whether the password is valid or not with the help of a few conditions.

Primary conditions for password validation:

1. Minimum 8 characters.
2. The alphabet must be between [a-z]
3. At least one alphabet should be of Upper Case [A-Z]
4. At least 1 number or digit between [0-9].
5. At least 1 character from [ _ or @ or $ ].

Examples:

Input : R@m@_f0rtu9e$
Output : Valid Password

Input : Rama_fortune$
Output : Invalid Password
Explanation: Number is missing

Input : Rama#fortu9e 
Output : Invalid Password
Explanation: Must consist from _ or @ or $

Way 1:

Here we have used the re module that provides support for regular expressions in Python. Along with this the re.search() method returns False (if the first parameter is not found in the second parameter) This method is best suited for testing a regular expression more than extracting data. We have used the re.search() to check the validation of alphabets, digits, or special characters. To check for white spaces we use the “\s” which comes in the module of the regular expression. 

Python3

# Python program to check validation of password
# Module of regular expression is used with search()
import re
password = "R@m@_f0rtu9e$"
flag = 0
while True:
    if (len(password)<=8):
        flag = -1
        break
    elif not re.search("[a-z]", password):
        flag = -1
        break
    elif not re.search("[A-Z]", password):
        flag = -1
        break
    elif not re.search("[0-9]", password):
        flag = -1
        break
    elif not re.search("[_@$]" , password):
        flag = -1
        break
    elif re.search("\s" , password):
        flag = -1
        break
    else:
        flag = 0
        print("Valid Password")
        break

if flag == -1:
    print("Not a Valid Password ")

Output

Valid Password

Time complexity: O(n), where n is the length of the password string.
Auxiliary space: O(1), as we are using only a few variables to store intermediate results.

Way 2:

Python3

l, u, p, d = 0, 0, 0, 0
s = "R@m@_f0rtu9e$"
if (len(s) >= 8):
    for i in s:

        # counting lowercase alphabets
        if (i.islower()):
            l+=1

        # counting uppercase alphabets
        if (i.isupper()):
            u+=1

        # counting digits
        if (i.isdigit()):
            d+=1

        # counting the mentioned special characters
        if(i=='@'or i=='$' or i=='_'):
            p+=1
if (l>=1 and u>=1 and p>=1 and d>=1 and l+p+u+d==len(s)):
    print("Valid Password")
else:
    print("Invalid Password")

Output

Valid Password

Time complexity: O(n) where n is the length of the input string s. 
Auxiliary space: O(1) as it only uses a few variables to store the count of various characters.

Way 3: Without using any built-in method

Python3

l, u, p, d = 0, 0, 0, 0
s = "R@m@_f0rtu9e$"
capitalalphabets="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
smallalphabets="abcdefghijklmnopqrstuvwxyz"
specialchar="$@_"
digits="0123456789"
if (len(s) >= 8):
    for i in s:

        # counting lowercase alphabets
        if (i in smallalphabets):
            l+=1

        # counting uppercase alphabets
        if (i in capitalalphabets):
            u+=1

        # counting digits
        if (i in digits):
            d+=1

        # counting the mentioned special characters
        if(i in specialchar):
            p+=1
if (l>=1 and u>=1 and p>=1 and d>=1 and l+p+u+d==len(s)):
    print("Valid Password")
else:
    print("Invalid Password")

Output

Valid Password

Time complexity : O(n), where n is the length of the input string s. 
Auxiliary space : O(1), as here only few variables are used to store the intermediate results.