Unable to understand a statement in an existing code

[deanhystad]

This is a list comprehension. It is a compact way of writing this:

temp = []
for word in tokens:
    if word.isalpha()
        temp.append(word)
tokens = temp

tokens = [] says the resulting list is assigned to "tokens".
[word for word in tokens] says the list is going to be made up of words from the original "tokens".
if isalpha(word) says only include words that are "isalpha".