Creating basic Python function to test if string password meets length requirements and contains special characters and digits

Question

I am a beginner in Python (using python3), and just learning to write basic functions. I am trying to solve the following problem: Write a function that takes a string as input and it returns whether the string is a valid password (the return value is True) or not (the return value is False). A string is a valid password if it:

1. contains least 1 number between 0 and 9, and
2. contains at least 1 character from the list ['$','#','@','.','!','?','<','>'] and
3. has a minimum length of at least 6 characters.

As you can see below I wrote three very basic functions which address the three conditions above separately. I understand that there are more advanced functions such as regex that would take care of this, but would like to stick to the basics.

I would like to create a fourth function which runs the list of passwords through this functions and then determines whether the string is valid or not. I am unable to create this function properly and would really appreciate some help. Thanks!

    passwords_lst = ['ilikeplums!','plum2020','a2b3?','applesaretasty','plum!','plum5','apple','1234','!p1umsareblue'] #list of passwords for testing

    #function for checking if password contains special chars
    def check_specialchar(pwd):
        spec_char_lst=['$','#','@','.','!','?','<','>']
        result=any(elem in spec_char_lst for elem in pwd)
        if result is True:
            print("Has special charactrs")
        else: 
            print("No special characters")
        return pwd
    for password in passwords_lst: #testing with actual list
        print(check_specialchar(password))

    #function for checking if length password>6
    def check_length(pwd):
        if len(pwd)>=6:     
            print("all ok")
        else:
            print("length is less than 6")
        return pwd
    for password in passwords_lst:  #testing with actual list
        print(check_length(password))


    #function for checking if password has at least one digit
    def checkif_digit(pwd):
        digit_count=0
        for char in pwd:
            if char.isdigit():
                digit_count=digit_count+1 #print("Has digits")
        print(digit_count)
            #else:
                #print("No special characters")
        if digit_count>0:
            print("Has at least one digit")
        return pwd
    for password in passwords_lst:  #testing with actual list

        print(checkif_digit(password))

#function for calling all three tests/functions created above and checking if passwords meet all three conditions
def check_pwd(pwd):
    for element in pwd:

    return element
print(check_pwd(passwords_lst))

Answer 1

Using your script as a starting point, I've modified functions to return either True or False depending on whether or not certain conditions are met.

def check_specialchar(pwd):
    '''return True if contains special chars, else False'''
    spec_char_lst = ["$", "#", "@", ".", "!", "?", "<", ">"]
    return any(elem in spec_char_lst for elem in pwd)


def check_length(pwd):
    '''return True if len >= 6, else False'''
    return len(pwd) >= 6


def checkif_digit(pwd):
    '''return True if 1 digit or more, else False'''
    return any(char.isdigit() for char in pwd)


def check_pwd(pwds):

    """
    return a list containing only valid passwords
    """
    res = []
    for pwd in pwds:
        if check_length(pwd) and check_length(pwd) and checkif_digit(pwd):
            res.append(pwd)
    return res

Here is an example input and output using passwords_lst.

>>> check_pwd(passwords_lst)
['plum2020', '!p1umsareblue']

Answer 2

• Given the code you already have
  • I added a print statement to each function to indicate which test is running
  • Returns True if test passed
  • I mostly left the existing functions as you wrote them.
• Call the other 3 functions from check_pwd
  • Pass the list to the function and iterate through the values to check them.

#function for checking if password contains special chars
def check_specialchar(pwd):
    spec_char_lst=['$','#','@','.','!','?','<','>']
    result=any(elem in spec_char_lst for elem in pwd)
    print('Special Characters Check:')
    if result:
        print("Has special charactrs")
        return True
    else: 
        print("No special characters")


#function for checking if length password>6
def check_length(pwd):
    print('Length Check:')
    if len(pwd)>=6:     
        print("all ok")
        return True
    else:
        print("length is less than 6")


#function for checking if password has at least one digit
def checkif_digit(pwd):
    print('Digit Check:')
    digit_count=0
    for char in pwd:
        if char.isdigit():
            digit_count=digit_count+1 
    if digit_count>0:
        print(f"Digit count: {digit_count}")
        return True
    else:
        print("No digits")


def check_pwd(pwd_list):
    for pwd in pwd_list:
        lines = '-'*30
        print(f'{lines}\nTesting: {pwd}')
        s = check_specialchar(pwd)
        l = check_length(pwd)
        d = checkif_digit(pwd)

        print(f'Passed all checks: {all([s, l, d])}')



passwords_lst = ['ilikeplums!','plum2020','a2b3?','applesaretasty','plum!','plum5','apple','1234','!p1umsareblue', '!thistesttopassall3'] #list of passwords for testing

check_pwd(passwords_lst)

Output of running the function

------------------------------
Testing: ilikeplums!
Special Characters Check:
Has special charactrs
Length Check:
all ok
Digit Check:
No digits
Passed all checks: False
------------------------------
Testing: plum2020
Special Characters Check:
No special characters
Length Check:
all ok
Digit Check:
Digit count: 4
Passed all checks: False
------------------------------
Testing: a2b3?
Special Characters Check:
Has special charactrs
Length Check:
length is less than 6
Digit Check:
Digit count: 2
Passed all checks: False
------------------------------
Testing: applesaretasty
Special Characters Check:
No special characters
Length Check:
all ok
Digit Check:
No digits
Passed all checks: False
------------------------------
Testing: plum!
Special Characters Check:
Has special charactrs
Length Check:
length is less than 6
Digit Check:
No digits
Passed all checks: False
------------------------------
Testing: plum5
Special Characters Check:
No special characters
Length Check:
length is less than 6
Digit Check:
Digit count: 1
Passed all checks: False
------------------------------
Testing: apple
Special Characters Check:
No special characters
Length Check:
length is less than 6
Digit Check:
No digits
Passed all checks: False
------------------------------
Testing: 1234
Special Characters Check:
No special characters
Length Check:
length is less than 6
Digit Check:
Digit count: 4
Passed all checks: False
------------------------------
Testing: !p1umsareblue
Special Characters Check:
Has special charactrs
Length Check:
all ok
Digit Check:
Digit count: 1
Passed all checks: True
------------------------------
Testing: !thistesttopassall3
Special Characters Check:
Has special charactrs
Length Check:
all ok
Digit Check:
Digit count: 1
Passed all checks: True

Answer 3

You can make each function return a boolean, then use the all() method to see if each function returned True for the password:

def check_specialchar(pwd):
    if any(c in '$#@.!?<>' for c in pwd):
        print("Has special charactrs")
        return True
    else: 
        print("No special characters")

def checkif_digit(pwd):
    if any(c in "1234567890" for c in pwd):
        print('Has at least one digit')
        return True
    else:
        print('Doesn\'t have digits')

def check_length(pwd):
    if len(pwd) > 5:
        print("length is okay")
        return True
    else:
        print("length is less than 6")

def check_pwd(pwd):
    if all([check_specialchar(pwd),checkif_digit(pwd),check_length(pwd)]):
        print("Good Password")
    else:
        print("Bad Password")

Test runs:

Input:

check_pwd("dh756dsdf")
print()
check_pwd("sdfg45?")

Output:

No special characters
Has at least one digit
length is okay
Bad Password

Has special charactrs
Has at least one digit
length is okay
Good Password