Removing a char from String, what's a more efficient way to do this? [duplicate]

Question

I'm currently studying Python 2.7 from an online course. One of the problems is I have to remove a char from a string based from a list of chars.

What I did was:

def getAvailableLetters(letters):

    alphabet = string.ascii_lowercase
    reduced_alphabet = ''

    for char in alphabet:
        if char not in lettersGuessed:
            reduced_alphabet += char

    return reduced_alphabet

I've learned that there's no such thing as a string method to directly remove a char from a string as they are immutable, so I came up with this. I've successfully submitted a correct answer, but I'm not quite satisfied with it as I feel like there's a more efficient way to do it.

Answer 1

Fastest way would be to use str.translate here:

>>> lettersGuessed = ['a', 'b', 'c']
>>> 'wedqwdasdasccdshjasdcas'.translate(None, ''.join(lettersGuessed))
'wedqwdsdsdshjsds'

if lettersGuessed is already a string then remove the ''.join call.

Timing results compared to str.join and filter, taken from @thefourtheye's solution:

def getAvailableLetters2(lettersGuessed):
    return string.ascii_lowercase.translate(None, lettersGuessed)

from timeit import timeit
print 'filter-->', timeit("getAvailableLetters('Welcome')", setup="from __main__ import getAvailableLetters")
print '.join-->', timeit("getAvailableLetters1('Welcome')",setup="from __main__ import getAvailableLetters1")
print 'trans-->', timeit("getAvailableLetters2('Welcome')",setup="from __main__ import getAvailableLetters2")

Output:

filter--> 6.49355100548
.join--> 4.02496357229
trans--> 0.69938109531