Question

I have a question about list concatenation in Python, I have this piece of code:

def lista():
    word = sys.argv[1]
    l = []
    m = []
    for file_name in sys.argv[2:]:
        with open(file_name, "r") as f:
            for line in f:
                l + [len(re.findall(word, line))] #doesn't work
                m.append(len(re.findall(word, line))) #works
    print l
    print m
    return l 

when I run this function I always get empty list l, but there are elements in m, why l+[elem] doesen’t work for me?

Answer 1

You are never assigning a new value to l. You should use assignment.
Try calling l = l + [len(re.findall(word,line))]

EDIT: another option is to use the += opertor: l+=[len(re.findall(word,line))]