Time complexity of os.walk in Python

Question

I\'ve to calculate the time-complexity of an algorithm, but in it I\'m calling os.walk which I can\'t consider as a single operation but many.

The sources of os.wal

Answer 1

Well... let's walk through the source :)

Docs: http://docs.python.org/2/library/os.html#os.walk

def walk(top, topdown=True, onerror=None, followlinks=False):
    islink, join, isdir = path.islink, path.join, path.isdir

    try:
        # Note that listdir and error are globals in this module due
        # to earlier import-*.


        # Should be O(1) since it's probably just reading your filesystem journal
        names = listdir(top)
    except error, err:
        if onerror is not None:
            onerror(err)
        return

    dirs, nondirs = [], []


    # O(n) where n = number of files in the directory
    for name in names:
        if isdir(join(top, name)):
            dirs.append(name)
        else:
            nondirs.append(name)

    if topdown:
        yield top, dirs, nondirs

    # Again O(n), where n = number of directories in the directory
    for name in dirs:
        new_path = join(top, name)
        if followlinks or not islink(new_path):

            # Generator so besides the recursive `walk()` call, no additional cost here.
            for x in walk(new_path, topdown, onerror, followlinks):
                yield x
    if not topdown:
        yield top, dirs, nondirs

Since it's a generator it all depends on how far you walk the tree, but it looks like O(n) where n is the total number of files/directories in the given path.