python - How do you filter a string to only contain letters?

Question

How do I make a function where it will filter out all the non-letters from the string? For example, letters("jajk24me") will return back "jajkme". (It needs to be a for loop) and will string.isalpha() function help me with this?

My attempt:

def letters(input):
    valids = []
    for character in input:
        if character in letters:
            valids.append( character)
    return (valids)

Answer 1

If it needs to be in that for loop, and a regular expression won't do, then this small modification of your loop will work:

def letters(input):
    valids = []
    for character in input:
        if character.isalpha():
            valids.append(character)
    return ''.join(valids)

(The ''.join(valids) at the end takes all of the characters that you have collected in a list, and joins them together into a string. Your original function returned that list of characters instead)

You can also filter out characters from a string:

def letters(input):
    return ''.join(filter(str.isalpha, input))

or with a list comprehension:

def letters(input):
    return ''.join([c for c in input if c.isalpha()])

or you could use a regular expression, as others have suggested.