Foundations of Python Network Programming 978-1-4302-3004-5

CHAPTER 17 ■ FTP
f.login()
f.cwd('/pub/academic/astronomy/')
entries = []
f.dir(entries.append)
print "%d entries:" % len(entries)
for entry in entries:
» print entry
f.quit()
Notice that the filenames are in a convenient format for automated processing — a bare list of
filenames — but that is no extra information. Contrast the bare list of file names we saw earlier with the
output from Listing 17–8, which uses dir():
$ python dir.py
13 entries:
-rw-r--r-- 1 (?) » (?) » » 750 Feb 14 1994 INDEX
-rw-r--r-- 1 root » bin » » 135 Feb 11 1999 README
-rw-r--r-- 1 (?) » (?) » 341303 Oct 2 1992 ephem_4.28.tar.Z
drwxr-xr-x 2 (?) » (?) » » 4096 Feb 11 1999 hawaii_scope
drwxr-xr-x 2 (?) » (?) » » 4096 Feb 11 1999 incoming
-rw-r--r-- 1 (?) » (?) » » 5983 Oct 2 1992 jupitor-moons.shar.Z
-rw-r--r-- 1 (?) » (?) » » 1751 Oct 2 1992 lunar.c.Z
-rw-r--r-- 1 (?) » (?) » » 8078 Oct 2 1992 lunisolar.shar.Z
-rw-r--r-- 1 (?) » (?) » » 64209 Oct 2 1992 moon.shar.Z
drwxr-xr-x 2 (?) » (?) » » 4096 Jan 6 1993 planetary
-rw-r--r-- 1 (?) » (?) » 129969 Oct 2 1992 sat-track.tar.Z
-rw-r--r-- 1 (?) » (?) » » 16504 Oct 2 1992 stars.tar.Z
-rw-r--r-- 1 (?) » (?) » 410650 Oct 2 1992 xephem.tar.Z
The dir() method takes a function that it calls for each line, delivering the directory listing in pieces
just like retrlines() delivers the contents of particular files. Here, we simply supply the append()
method of our plain old Python entries list.
Detecting Directories and Recursive Download
If you cannot guarantee what information an FTP server might choose to return from its dir()
command, how are you going to tell directories from normal files—an essential step to downloading
entire trees of files from the server?
The answer, shown in Listing 17–9, is to simply try a cwd() into every name that nlst() returns and,
if you succeed, conclude that the entity is a directory! This sample program does not do any actual
downloading; instead, to keep things simple (and not flood your disk with sample data), it simply prints
out the directories it visits to the screen.
Listing 17–9. Trying to Recurse into Directories
#!/usr/bin/env python
# Recursive downloader - Chapter 17 - recursedl.py
import os, sys
from ftplib import FTP, error_perm
def walk_dir(f, dirpath):
» original_dir = f.pwd()
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