I'm getting occasional not reproducable errors (with the same markdown source) when running on Appengine:

Traceback (most recent call last): [...] File "/base/data/home/apps/.../deps/markdown/__init__.py", line 375, in convert newRoot = treeprocessor.run(root) File "/base/data/home/apps/.../deps/markdown/treeprocessors.py", line 330, in run self.ancestors.pop() IndexError: pop from empty list 

I'm having threading enabled (GAE default), and TreeProcessor has a global ancestors stack. So presumably this crashes because simultaneous threads run the markdown processor. I can't find anything in the docs whether python-markdown is supposed to be thread safe, so thats either a documentation request or a bug ;-)