BUG: GH24011 - Rich comparisons of Timestamps now return NotImplemented

pandas/_libs/tslibs/timestamps.pyx

@@ -240,12 +240,7 @@ cdef class _Timestamp(datetime):
                     return PyObject_RichCompare(np.array([self]), other, op)
                 return PyObject_RichCompare(other, self, reverse_ops[op])
             else:
-                if op == Py_EQ:
-                    return False
-                elif op == Py_NE:
-                    return True
-                raise TypeError('Cannot compare type %r with type %r' %
-                                (type(self).__name__, type(other).__name__))
+                return NotImplemented
 
         self._assert_tzawareness_compat(other)
         return cmp_scalar(self.value, ots.value, op)

pandas/tests/tslibs/test_tslib.py

@@ -21,3 +21,33 @@ def test_normalize_date():
 
     actual = tslibs.normalize_date(value)
     assert actual == datetime(2007, 10, 1)
+
+
+def test_rich_comparison_with_unsupported_type():
+    # See https://github.com/pandas-dev/pandas/issues/24011
+
+    class Inf:
+        def __lt__(self, o):
+            return False
+
+        def __le__(self, o):
+            return isinstance(o, Inf)
+
+        def __gt__(self, o):
+            return not isinstance(o, Inf)
+
+        def __ge__(self, o):
+            return True
+
+        def __eq__(self, o):
+            return isinstance(o, Inf)
+
+    timestamp = tslibs.Timestamp('2018-11-30')
+
+    # Comparison works if compared in *that* order, because
+    # magic method is called on Inf
+    assert Inf() > timestamp
+    assert not (Inf() < timestamp)
+
+    # ... but used to not work when magic method is called on Timestamp
+    assert timestamp < Inf()