To add to bhadra's list of idiomatic guides:
Checkout Anthony Baxter's presentation on Effective Python Programming (from OSON 2005).
An excerpt:
# dict's setdefault method turns this:
if key in dictobj:
dictobj[key].append(val)
else:
dictobj[key] = [val]
# into this:
dictobj.setdefault(key,[]).append(val)