Bugfix timedelta notimplemented eq

doc/source/whatsnew/v0.24.0.txt

@@ -479,6 +479,7 @@ all-``NaT``.  This is for compatibility with ``TimedeltaIndex`` and
 Previous Behavior:
 
 .. code-block:: ipython
+- Comparing :class:`Timedelta` with unknown types now return NotImplemented instead of False (:issue:`20829`)
 
     In [4]: df = pd.DataFrame([pd.Timedelta(days=1)])
 

pandas/_libs/tslibs/timedeltas.pyx

@@ -724,27 +724,12 @@ cdef class _Timedelta(timedelta):
                     if is_timedelta64_object(other):
                         other = Timedelta(other)
                     else:
-                        if op == Py_EQ:
-                            return False
-                        elif op == Py_NE:
-                            return True
-
-                        # only allow ==, != ops
-                        raise TypeError('Cannot compare type {cls} with '
-                                        'type {other}'
-                                        .format(cls=type(self).__name__,
-                                                other=type(other).__name__))
+                        return NotImplemented
                 if util.is_array(other):
                     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 {cls} with type {other}'
-                                .format(cls=type(self).__name__,
-                                        other=type(other).__name__))
+                return NotImplemented
 
         return cmp_scalar(self.value, ots.value, op)
 

pandas/tests/scalar/timedelta/test_timedelta.py

@@ -42,8 +42,10 @@ def test_ops_error_str(self):
             with pytest.raises(TypeError):
                 left + right
 
-            with pytest.raises(TypeError):
-                left > right
+            # GH 20829: python 2 comparison naturally does not raise TypeError
+            if compat.PY3:
+                with pytest.raises(TypeError):
+                    left > right
 
             assert not left == right
             assert left != right
@@ -103,6 +105,54 @@ def test_compare_timedelta_ndarray(self):
         expected = np.array([False, False])
         tm.assert_numpy_array_equal(result, expected)
 
+    def test_compare_custom_object(self):
+        # GH20829
+        class CustomClass(object):
+
+            def __init__(self, cmp_result=None):
+                self.cmp_result = cmp_result
+
+            def generic_result(self):
+                if self.cmp_result is None:
+                    return NotImplemented
+                else:
+                    return self.cmp_result
+
+            def __eq__(self, other):
+                return self.generic_result()
+
+            def __gt__(self, other):
+                return self.generic_result()
+
+        t = Timedelta('1s')
+
+        assert not (t == "string")
+        assert not (t == 1)
+        assert not (t == CustomClass())
+        assert not (t == CustomClass(cmp_result=False))
+
+        assert t < CustomClass(cmp_result=True)
+        assert not (t < CustomClass(cmp_result=False))
+
+        assert t == CustomClass(cmp_result=True)
+
+    @pytest.mark.skipif(compat.PY2,
+                        reason="python 2 does not raise TypeError for \
+                               comparisons of different types")
+    @pytest.mark.parametrize("val", [
+        "string", 1])
+    def test_compare_unknown_type(self, val):
+        # GH20829
+        t = Timedelta('1s')
+        with pytest.raises(TypeError):
+            t >= val
+        with pytest.raises(TypeError):
+            t > val
+        with pytest.raises(TypeError):
+            t <= val
+        with pytest.raises(TypeError):
+            t < val
+
 
 class TestTimedeltas(object):