How to remove a list of characters from another list?

Question

I've been able to isolate the list (or string) of characters I want excluded from a user entered string. But I don't see how to then remove all these unwanted characters. After I do this, I think I can try joining the user string so it all becomes one alphabet input like the instructions say.

Instructions:

• Remove all non-alpha characters
• Write a program that removes all non-alpha characters from the given input.

For example, if the input is:

-Hello, 1 world$!

the output should be:

Helloworld

My code:

userEntered = input()
makeList = userEntered.split()
def split(userEntered):
    return list(userEntered)
    
    
if userEntered.isalnum() == False:
    for i in userEntered:
        if i.isalpha() == False:
            #answer = userEntered[slice(userEntered.index(i))]
           reference = split(userEntered)
           excludeThis = i
           print(excludeThis)
    

When I print excludeThis, I get this as my output:

-
,
 
1
 
$
!

So I think I might be on the right track. I need to figure out how to get these characters out of the user input.

Answer 1

Loop over the input string. If the character is alphabetic, add it to the result string.

userEntered = input()
result = ''
for char in userEntered:
    if char.isalpha():
        result += char
print(result)

This can also be done with a regular expression:

import re

userEntered = input()
result = re.sub(r'[^a-z]', '', userEntered, flags=re.I)

The regexp [^a-z] matches anything except an alphabetic character. The re.I flag makes it case-insensitive. These are all replaced with an empty string, which removes them.