most recently opened URL in self.openedurl of the URLopener instance.
This doesn't really work if multiple threads share the same opener
instance!

Fix: openedurl was actually simply the type prefix (e.g. "http:")
followed by the rest of the URL; since the rest of the URL is
available and the type is effectively determined by where you are in
the code, I can reconstruct the full URL easily, e.g. "http:" + url.

- use the tempcache in the open() method, too.

- use the "unwrap"ped url as key for the tempcache.

(2) Provisional hack to avoid dying when trying to turn echo on or off
on Macs, where os.system() doesn't exist.

would set the transfer to text mode instead of the specified mode.

retrieving files from the same host and directory, you had to close
the previous instance before opening a new one; and retrieving a
non-existent file would return an empty file.  (The latter fix relies
on maybe an undocumented property of NLST -- NLST of a file returns
just that file, while NLST of a non-existent file returns nothing.  A
side effect, unfortunately, seems to be that now ftp-retrieving an
*empty* directory may fail.  Ah well.)

is indeed a dictionary (or a mapping).

problems with this module, even if an instance of a derived class is
kept alive longer than the urllib module itself...

Use "re" module, making it threadsafe.

a shared class variable -- but each instance will attempt to clean it
up entirely ob cleanup).

Sjoerd: add separate administration of temporary files created y
URLopener.retrieve() so cleanup can properly remove them.  The old
code removed everything in tempcache which was a bad idea if the user
had passed a non-temp file into it.  (I added a line to delete the
tempcache in cleanup() -- it still seems to make sense.)

Jack: in basejoin(), interpret relative paths starting in "../".  This
is necessary if the server uses symbolic links.

that multiple retrievals using the same connection will work.

This leaves open the more general problem that after
    f = urlopen("ftp://...")
f must be closed before another retrieval from the same host should be
attempted.

Windows/Mac).

than just the four.

Also folded some long lines.

guarded by 'if self.tempcache', to reduce the likelihood of this
causing an exception when invoked during __del__...

for form field values.

IOError, keep the traceback.

Fix 1: add a method geturl() to the file-like object returned by urlopen().
Fix 2: treat http error 301 the same as error 302.

Correctly handle a URL containing user:password@host when using a proxy.

is forgiving about semi-numeric port numbers, and allows you to specify
a default port (default is -1, None returned for nonnumeric port).