Can't wrap my head around how to remove a list of characters from another list-CodePudding

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 it out how to get these characters out of the user input. Any help is appreciated.

CodePudding user response：

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.

CodePudding user response：

There's basically two main parts to this: distinguish alpha from non-alpha, and get a string with only the former. If isalpha() is satisfactory for the former, then that leaves the latter. My understanding is that the solution that is considered most Pythonic would be to join a comprehension. This would like this:

''.join(char for char in userEntered if char.isalpha())

BTW, there are several places in the code where you are making it more complicated than it needs to be. In Python, you can iterate over strings, so there's no need to convert userEntered to a list. isalnum() checks whether the string is all alphanumeric, so it's rather irrelevant (alphanumeric includes digits). You shouldn't ever compare a boolean to True or False, just use the boolean. So, for instance, if i.isalpha() == False: can be simplified to just if not i.isalpha():.