how to write a regex pattern for email and password?

Question

i have problem with writing regex pattern for following statements. i think i have problem with pattern of email.

for email:

1. domain should be end with google.com or (nothing or any characters).go
2. at least we should have 3 numbers and all letters should be lowercase
3. in email address we just have one $

for password:

1. at least it should be 8 characters
2. it should has at least one Uppercase letter and at least one number
3. it should has at least one of these characters !@#$%^

email_pattern = re.compile(r'^((?=.*\$)((?=.*[0-9]){3,})(?=.*[a-z]*))(\@)((google\.com)|([a-z0-9\!\@\#\%\^\&]*\.go))$')

pass_pattern = re.compile(r'((?=.*(\!|\@|\#|\$|\%|\^))(?=.*[A-Z])(?=.*[0-9])(?=.*[a-z])(?=.*[a-zA-z0-9!@#$%^]*)){8,}')

Answer 1

In my opinion, there is no need to use this kind of regular expression. They are scary, difficult to understand and difficult to customize. If you need to validate email and password, then why not break it down into several steps? Yes, there will probably be more code, but further interaction with it will become easier. If necessary, you can remove one of the checks or add a new one without touching the others. Read something about the principle of "Divide and Conquer".

Here is one of the easily customizable and readable solutions to your problem:

import re


def email_is_valid(email:str) -> bool:
    ''' Returns True if email is valid and False if it's not
    '''
    conditions = [
        # Checking for correct ending and forbidden characters
        re.fullmatch(r'[a-z0-9$]{1,}((@google.com)|(\.go))$', email),
        # Checking for at least three digits
        re.search(r'(?=(?:.*\d){3,})', email),
        # Checking for only one '$'
        email.count('$') == 1,
    ]
    for condition in conditions:
        if not condition:
            return False
    return True


def password_is_valid(password:str) -> bool:
    ''' Returns True if password is valid and False if it's not
    '''
    conditions = [
        # Checking the length and presence of forbidden characters
        re.fullmatch(r'[A-Za-z0-9!@#$%^]{8,}', password),
        # Looking for at least one of these characters !@#$%^
        re.search(r'[!@#$%^]{1,}', password), 
        # Looking for at least one Uppercase letter
        re.search(r'[A-Z]{1,}', password),
    ]
    for condition in conditions:
        if not condition:
            return False
    return True

And here is how the use of these functions will look like. Easy to read.

import email_is_valid, password_id_valid


if email_is_valid(your_email):
    ...

if password_id_valid(your_password):
    ...