Issue 3051: make pure python code pass the same tests as the C version.

Lib/heapq.py

@@ -133,6 +133,11 @@ from itertools import islice, repeat, count, imap, izip, tee, chain
 from operator import itemgetter
 import bisect
 
+def cmp_lt(x, y):
+    # Use __lt__ if available; otherwise, try __le__.
+    # In Py3.x, only __lt__ will be called.
+    return (x < y) if hasattr(x, '__lt__') else (not y <= x)
+
 def heappush(heap, item):
     """Push item onto heap, maintaining the heap invariant."""
     heap.append(item)
@@ -167,7 +172,7 @@ def heapreplace(heap, item):
 
 def heappushpop(heap, item):
     """Fast version of a heappush followed by a heappop."""
-    if heap and heap[0] < item:
+    if heap and cmp_lt(heap[0], item):
         item, heap[0] = heap[0], item
         _siftup(heap, 0)
     return item
@@ -215,11 +220,10 @@ def nsmallest(n, iterable):
         pop = result.pop
         los = result[-1]    # los --> Largest of the nsmallest
         for elem in it:
-            if los <= elem:
-                continue
-            insort(result, elem)
-            pop()
-            los = result[-1]
+            if cmp_lt(elem, los):
+                insort(result, elem)
+                pop()
+                los = result[-1]
         return result
     # An alternative approach manifests the whole iterable in memory but
     # saves comparisons by heapifying all at once.  Also, saves time
@@ -240,7 +244,7 @@ def _siftdown(heap, startpos, pos):
     while pos > startpos:
         parentpos = (pos - 1) >> 1
         parent = heap[parentpos]
-        if newitem < parent:
+        if cmp_lt(newitem, parent):
             heap[pos] = parent
             pos = parentpos
             continue
@@ -295,7 +299,7 @@ def _siftup(heap, pos):
     while childpos < endpos:
         # Set childpos to index of smaller child.
         rightpos = childpos + 1
-        if rightpos < endpos and not heap[childpos] < heap[rightpos]:
+        if rightpos < endpos and not cmp_lt(heap[childpos], heap[rightpos]):
             childpos = rightpos
         # Move the smaller child up.
         heap[pos] = heap[childpos]