Python's urllib module conveniently handles a great many bits of fetching URLs for you, including HTTP basic authentication. Unfortunately it does this by pausing everything to 'ask the user for the required information on the controlling terminal' (to more or less quote from the documentation). This is generally not the most useful behavior in the world, and can even be rather disconcerting.

(A more sensible default behavior would have been to either raise an exception or return a HTTP 'authentication required' status.)

As a result, all of my urllib-using programs start off by neutering this behavior, so that if I ask them to deal with a stray URL that requires HTTP basic authentication they'll just fail. To do this, you need to subclass FancyURLopener and supply your own get_user_passwd routine that does nothing:

from urllib import FancyURLopener

class MyOpener(FancyURLopener):
  def get_user_passwd(self, h, r, c_c = 0)
    return None, None

This is covered in the urllib documentation, sort of, but not even the urllib docstrings tell you what the return value should be. Apparently you are just supposed to read the source.

(Technically you can supply a do-nothing prompt_user_passwd routine instead, with the same effect, but I prefer to just neuter the whole thing.)

This is not the only peculiar thing urllib does. For another example, it turns basically every problem into IOError exceptions, generally in blithe disregard of their standard format. (And of course it is now far too late to fix this, because it would break backwards compatibility for everyone who has carefully worked around this.)

There's the urllib2 module as an alternative, but the length of its documentation makes my eyes glaze over. However, on some testing it seems to be reasonably simple to use, and as a bonus it does the right thing with HTTP basic authentication. I suspect that I should start switching my code over, and certainly use it for anything new I do.

(I still use urllib because I started with Python in the 1.5 days, when there was no urllib2. Technically we still have some machines with 1.5.2, but on those machines we just use a locally built version of 2.3.4.)