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

CHAPTER 17 ■ FTP
» try:
» » f.cwd(dirpath)
» except error_perm:
» » return # ignore non-directories and ones we cannot enter
» print dirpath
» names = f.nlst()
» for name in names:
» » walk_dir(f, dirpath + '/' + name)
» f.cwd(original_dir) # return to cwd of our caller
f = FTP('ftp.kernel.org')
f.login()
walk_dir(f, '/pub/linux/kernel/Historic/old-versions')
f.quit()
This sample program will run a bit slow—there are, it turns out, quite a few files in the old-versions
directory on the Linux Kernel Archive—but within a few dozen seconds, you should see the resulting
directory tree displayed on the screen:
$ python recursedl.py
/pub/linux/kernel/Historic/old-versions
/pub/linux/kernel/Historic/old-versions/impure
/pub/linux/kernel/Historic/old-versions/old
/pub/linux/kernel/Historic/old-versions/old/corrupt
/pub/linux/kernel/Historic/old-versions/tytso
By adding a few print statements, you could supplement this list of directories by displaying every
one of the files that the recursive process is (slowly) discovering. And by adding another few lines of
code, you could be downloading the files themselves to corresponding directories that you create locally.
But the only really essential logic for a recursive download is already operating in Listing 17–9: the only
foolproof way to know if an entry is a directory that you are allowed to enter is to try running cwd()
against it.
Creating Directories, Deleting Things
Finally, FTP supports file deletion, and supports both the creation and deletion of directories. These
more obscure calls are all described in the ftplib documentation:
• delete(filename) will delete a file from the server.
• mkd(dirname) attempts to create a new directory.
• rmd(dirname) will delete a directory; note that most systems require the directory
to be empty first.
• rename(oldname, newname) works, essentially, like the Unix command mv: if both
names are in the same directory, the file is essentially re-named; but if the
destination specifies a name in a different directory, then the file is actually
moved.
Note that these commands, like all other FTP operations, are performed more or less as though you
were really logged on to the remote server command line as the same username with which you logged
into FTP—and the chances of your having permission to manipulate files on a given server are lower
than being able to download files, or even to create new files in an upload directory. Still, it is because of
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