How to only allow digits, letters, and certain characters in a string in Python?

Question

I want to make a password checker but how do I make it so I can write an error if there are characters other than digits, upper/lowercase and (,),$,%,_/.

What I have so far:

import sys
import re
import string
import random

password = input("Enter Password: ")
length = len(password)
if length < 8:
    print("\nPasswords must be between 8-24 characters\n\n")
elif length > 24:
    print ("\nPasswords must be between 8-24 characters\n\n")

elif not re.match('[a-z]',password):
        print ('error')

Are you asking how to write a regex that matches the conditions you set? — thumbtackthief
– thumbtackthief, Commented Oct 17, 2017 at 20:35
You should learn the basics of regexes first. Open up your favourite search engine and search for something like "regex tutorial". — ForceBru
– ForceBru, Commented Oct 17, 2017 at 20:36
Here's a link that might be related to your question, stackoverflow.com/questions/41117733/… — Aswini
– Aswini, Commented Oct 17, 2017 at 20:38

Maksiks · Accepted Answer · 2023-08-24 19:08:09Z

3

You need to have a regular expression against which you will validate like this:

m = re.compile(r'[a-zA-Z0-9()$%_/.]*$')
if(m.match(input_string)):
     # Do something...
else:
     # Reject with your logic ...

edited Aug 24, 2023 at 19:08

Maksiks

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answered Oct 17, 2017 at 20:41

Gurvinder Singh

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Comments

thumbtackthief · Accepted Answer · 2017-10-17 20:37:08Z

1

Try

elif not re.match('^[a-zA-Z0-9()$%_/.]*$',password):

I can't tell if you want to allow commas. If so use ^[a-zA-Z0-9()$%_/.,]*$

edited Oct 17, 2017 at 20:37

thumbtackthief

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answered Oct 17, 2017 at 20:35

MisterMystery

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Comments

Sim Son · Accepted Answer · 2022-09-23 00:02:16Z

1

If you want to avoid using RegEx, you can try this self-explanatory solution

allowed_characters=['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','1','2','3','4','5','6','7','8','9','0','(',')','$','%','_','/']

password=input("enter password: ")
if any(x not in allowed_characters for x in password):
  print("error: invalid character")
else:
  print("no error")

edited Sep 23, 2022 at 0:02

answered Oct 17, 2017 at 21:06

Sim Son

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2 Comments

Alien426 Over a year ago

Very nice when you have few allowed characters and don't want to use RegEx. Thanks.

Ricky Levi Over a year ago

I would just replace allowed_characters with the built-in module import string where you can use allowed_characters = string.ascii_letters + string.digits + r'()$%_/.]*$' to be more readable.

Rob Bailey · Accepted Answer · 2017-10-17 20:52:39Z

0

With Python, you should be raising exceptions when something goes wrong:

if re.search(r'[^a-zA-Z0-9()$%_]', password):
    raise Exception('Valid passwords include ...(whatever)')

This searches for any character in the password that is not (^) in the set of characters defined between the square brackets.

edited Oct 17, 2017 at 20:52

answered Oct 17, 2017 at 20:46

Rob Bailey

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