BUG: GH24011 - Rich comparisons of Timestamps now return NotImplemented

doc/source/whatsnew/v0.25.0.rst

@@ -33,6 +33,9 @@ Backwards incompatible API changes
 
 .. _whatsnew_0250.api_breaking.utc_offset_indexing:
 
+- Rich comparisons involving :class:`~Timestamp.Timestamp` return ``NotImplemented`` instead of raising ``TypeError`` with unsupported objects (:issue:`24011`)
+
+
 Indexing with date strings with UTC offsets
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

pandas/_libs/tslibs/timestamps.pyx

@@ -239,26 +239,13 @@ cdef class _Timestamp(datetime):
                     if is_datetime64_object(other):
                         other = Timestamp(other)
                     else:
-                        if op == Py_EQ:
-                            return False
-                        elif op == Py_NE:
-                            return True
-
-                        # only allow ==, != ops
-                        raise TypeError('Cannot compare type %r with type %r' %
-                                        (type(self).__name__,
-                                         type(other).__name__))
+                        return NotImplemented
                 elif is_array(other):
                     # avoid recursion error GH#15183
                     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/scalar/timestamp/test_comparisons.py

@@ -166,3 +166,42 @@ def test_timestamp_compare_with_early_datetime(self):
         assert stamp >= datetime(1600, 1, 1)
         assert stamp < datetime(2700, 1, 1)
         assert stamp <= datetime(2700, 1, 1)
+
+
+def test_rich_comparison_with_unsupported_type():
+    # See https://github.com/pandas-dev/pandas/issues/24011
+
+    class Inf(object):
+        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 = 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)
+    assert Inf() != timestamp
+    assert not (Inf() == timestamp)
+    assert Inf() >= timestamp
+    assert not (Inf() <= timestamp)
+
+    # ... but used to not work when magic method is called on Timestamp
+    assert not (timestamp > Inf())
+    assert timestamp < Inf()
+    assert timestamp != Inf()
+    assert not (timestamp == Inf())
+    assert timestamp <= Inf()
+    assert not (timestamp >= Inf())