I misread a recent feedparser bug report and thought that the author had mistyped a bbcode- or wiki-formatted link. Consequently, I wasted time debugging the code.

Turns out, I wasted a lot of time, because I spent more than zero time debugging the code. Yes, zero time. I was using a conditional breakpoint when I should have been using pdb's post_mortem() (or pm() for short). I had no idea what post-mortem debugging was until I ran across Doug Hellmann's article on pdb. I barely finished reading the following two sentences before I alt-tabbed back and found the problem:

Debugging a failure after a program terminates is called post-mortem debugging. pdb supports post-mortem debugging through the pm() and post_mortem() functions.

So my debugging session should have looked like:

import feedparser  
import pdb  
feedparser.parse('offending-url')  
# huge traceback  
pdb.pm()

Pressing u a few times took me up the call stack, and then p uri printed out the offending...wait, that's what the bug reporter already told me.

The important thing here is that I discovered a time-saving tool. (And found a performance problem with feedparser: it calls _urijoin() hundreds of times for no discernible reason. Reducing that call volume may improve performance.) Learning is fun!