Question

The following gets the files, but they are not sorted.

    for fn in os.listdir(path):

        if fn[0] == '.':
            continue

        try:
            p = os.path.join(path, fn)
        except:
            continue

        s = os.lstat(p)

        if stat.S_ISDIR(s.st_mode):
            l.append((fn, build_tree(p)))
        elif stat.S_ISREG(s.st_mode):
            l.append((fn, s.st_size))

Answer 1

import operator

for fn in os.listdir(path):

    if fn[0] == '.':
        continue

    try:
        p = os.path.join(path, fn)
    except:
        continue

    s = os.lstat(p)

    if stat.S_ISDIR(s.st_mode):
        l.append((fn, build_tree(p)))
    elif stat.S_ISREG(s.st_mode):
        l.append((fn, s.st_size))

For ascending sort:

l.sort(key=operator.itemgetter(1))

For descending sort:

l.sort(key=operator.itemgetter(1), reverse=True)