Add functools.CmpToKey()

1 files changed, 45 insertions, 0 deletions

diff --git a/Lib/functools.py b/Lib/functools.py
index a54f030..d31b090 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -49,3 +49,48 @@ def wraps(wrapped,
     """
     return partial(update_wrapper, wrapped=wrapped,
                    assigned=assigned, updated=updated)
+
+def total_ordering(cls):
+    'Class decorator that fills-in missing ordering methods'
+    convert = {
+        '__lt__': [('__gt__', lambda self, other: other < self),
+                   ('__le__', lambda self, other: not other < self),
+                   ('__ge__', lambda self, other: not self < other)],
+        '__le__': [('__ge__', lambda self, other: other <= self),
+                   ('__lt__', lambda self, other: not other <= self),
+                   ('__gt__', lambda self, other: not self <= other)],
+        '__gt__': [('__lt__', lambda self, other: other > self),
+                   ('__ge__', lambda self, other: not other > self),
+                   ('__le__', lambda self, other: not self > other)],
+        '__ge__': [('__le__', lambda self, other: other >= self),
+                   ('__gt__', lambda self, other: not other >= self),
+                   ('__lt__', lambda self, other: not self >= other)]
+    }
+    roots = set(dir(cls)) & set(convert)
+    assert roots, 'must define at least one ordering operation: < > <= >='
+    root = max(roots)       # prefer __lt __ to __le__ to __gt__ to __ge__
+    for opname, opfunc in convert[root]:
+        if opname not in roots:
+            opfunc.__name__ = opname
+            opfunc.__doc__ = getattr(int, opname).__doc__
+            setattr(cls, opname, opfunc)
+    return cls
+
+def CmpToKey(mycmp):
+    'Convert a cmp= function into a key= function'
+    class K(object):
+        def __init__(self, obj, *args):
+            self.obj = obj
+        def __lt__(self, other):
+            return mycmp(self.obj, other.obj) < 0
+        def __gt__(self, other):
+            return mycmp(self.obj, other.obj) > 0
+        def __eq__(self, other):
+            return mycmp(self.obj, other.obj) == 0
+        def __le__(self, other):
+            return mycmp(self.obj, other.obj) <= 0
+        def __ge__(self, other):
+            return mycmp(self.obj, other.obj) >= 0
+        def __ne__(self, other):
+            return mycmp(self.obj, other.obj) != 0
+    return K