Exercise to implement some recursive directory scaning

ls.py

#!/usr/bin/env python3

import grp
import os
import pwd
import stat
import sys
import time

SIX_MONTHS = 6 * 30 * 86400

def ls(dir):
    print('%s:' % dir)
    entries = tuple((filename, os.stat(dir + '/' + filename)) for filename in os.listdir(dir))
    filtered_entries = []
    for entry in entries:
        filename = entry[0]
        if filename[0] != '.':
            filtered_entries.append(entry)

    total_size = sum((entry[1][stat.ST_SIZE] + 4095) // 4096 * 4 for entry in filtered_entries)
    print('total %d' % total_size)

    curr_time = time.time()

    sizes = [entry[1][stat.ST_SIZE] for entry in filtered_entries]
    if len(sizes) > 0:
        max_size = max(sizes)
    else:
        max_size = 0
    size_width = len('%d' % max_size)

    sorted_entries = sorted(filtered_entries, key=lambda e: e[0].lower())

    for entry in sorted_entries:
        filename = entry[0]
        filestat = entry[1]

        mode = filestat[stat.ST_MODE]
        num_links = filestat[stat.ST_NLINK]
        uid = filestat[stat.ST_UID]
        gid = filestat[stat.ST_GID]
        size = filestat[stat.ST_SIZE]
        mtime = filestat[stat.ST_MTIME]

        mode_str = ''
        mode_str += 'd' if stat.S_ISDIR(mode) else '-'
        mode_str += 'r' if mode & stat.S_IRUSR else '-'
        mode_str += 'w' if mode & stat.S_IWUSR else '-'
        mode_str += 'x' if mode & stat.S_IXUSR else '-'
        mode_str += 'r' if mode & stat.S_IRGRP else '-'
        mode_str += 'w' if mode & stat.S_IWGRP else '-'
        mode_str += 'x' if mode & stat.S_IXGRP else '-'
        mode_str += 'r' if mode & stat.S_IROTH else '-'
        mode_str += 'w' if mode & stat.S_IWOTH else '-'
        mode_str += 'x' if mode & stat.S_IXOTH else '-'

        uname = pwd.getpwuid(uid)[0]
        gname = grp.getgrgid(gid)[0]

        ltime = time.localtime(mtime)
        time_str = time.strftime('%b ', ltime)
        time_str += '%2d ' % ltime.tm_mday

        if mtime < curr_time - SIX_MONTHS or mtime > curr_time + SIX_MONTHS:
            time_str += time.strftime(' %Y', ltime)
        else:
            time_str += time.strftime('%H:%M', ltime)

        print('%s %d %-8s %-8s %*d %s %s' % (mode_str, num_links, uname, gname, size_width, size, time_str, filename))

    for entry in sorted_entries:
        filename = entry[0]
        filestat = entry[1]
        mode = filestat[stat.ST_MODE]
        if stat.S_ISDIR(mode):
            print()
            ls(dir + '/' + filename)

ls('.')