Putting a pleasant Python surprise to use

Although I've been programming in Python for a few years now, it keeps surprising me with little bits and pieces. Here's a neat Python language feature that I recently used for the first time (discovered originally through Bram Cohen's LiveJournal).

A common programming pattern is 'search for a something to work on, but stop if you don't find anything'. In Python one might write it something like this (taken more or less from DWiki's source):

found = False
for dir in utils.walk_to_root(curdir):
	page = dir.child("__readme")
	if page.exists():
		found = True
		break
if not found:
	return ''
# Go on to use the __readme file we found in some directory.

Python allows you to put 'else' conditions on loops (both for and while loops); the else condition is executed if the loop completed instead of being break'd from. This lets us simplify this pattern down to:

for dir in utils.walk_to_root(curdir):
	page = dir.child("__readme")
	if page.exists():
		break
else:
	return ''

If there's no __readme file to be found from the current directory up to the root, we just return nothing; otherwise, we'll process it. This DWiki code is the first occasion I've had to use this feature since I discovered it, and I'm pleased to finally have been able to.

(As you can now see, not all the entries in this blog are going to be long and meandering.)