Docstring nit.

Lib/heapq.py

@@ -311,7 +311,7 @@ except ImportError:
 def merge(*iterables):
     '''Merge multiple sorted inputs into a single sorted output.
 
-    Similar to sorted(itertools.chain(*iterables)) but returns an iterable,
+    Similar to sorted(itertools.chain(*iterables)) but returns a generator,
     does not pull the data into memory all at once, and assumes that each of
     the input streams is already sorted (smallest to largest).