The documentation for heapq.nsmallest and heapq.nlargest:

http://docs.python.org/3.3/library/heapq.html#heapq.nlargest

claim that they accept three arguments: n, iterable, and key=None.  In fact, the implementations of both these functions only accept two parameters: n and iterable.

I assume the right thing to do here is to remove the erroneous documentation, rather than implement this apparently-not-needed feature?