Revert pandas-dev#21394 (pandas-dev#24289)

* Revert pandas-dev#21394

* Typo fixup

Author: jbrockmendel

doc/source/whatsnew/v0.24.0.rst

@@ -1082,7 +1082,6 @@ Other API Changes
   has an improved ``KeyError`` message, and will not fail on duplicate column names with ``drop=True``. (:issue:`22484`)
 - Slicing a single row of a DataFrame with multiple ExtensionArrays of the same type now preserves the dtype, rather than coercing to object (:issue:`22784`)
 - :class:`DateOffset` attribute `_cacheable` and method `_should_cache` have been removed (:issue:`23118`)
-- Comparing :class:`Timedelta` to be less or greater than unknown types now raises a ``TypeError`` instead of returning ``False`` (:issue:`20829`)
 - :meth:`Categorical.searchsorted`, when supplied a scalar value to search for, now returns a scalar instead of an array (:issue:`23466`).
 - :meth:`Categorical.searchsorted` now raises a ``KeyError`` rather that a ``ValueError``, if a searched for key is not found in its categories (:issue:`23466`).
 - :meth:`Index.hasnans` and :meth:`Series.hasnans` now always return a python boolean. Previously, a python or a numpy boolean could be returned, depending on circumstances (:issue:`23294`).

pandas/_libs/tslibs/timedeltas.pyx

@@ -770,12 +770,26 @@ cdef class _Timedelta(timedelta):
                     if is_timedelta64_object(other):
                         other = Timedelta(other)
                     else:
-                        return NotImplemented
+                        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__))
                 if util.is_array(other):
                     return PyObject_RichCompare(np.array([self]), other, op)
                 return PyObject_RichCompare(other, self, reverse_ops[op])
             else:
-                return NotImplemented
+                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 cmp_scalar(self.value, ots.value, op)
 

pandas/tests/scalar/timedelta/test_timedelta.py

@@ -44,10 +44,8 @@ def test_ops_error_str(self):
             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
+            with pytest.raises(TypeError):
+                left > right
 
             assert not left == right
             assert left != right
@@ -107,9 +105,12 @@ def test_compare_timedelta_ndarray(self):
         expected = np.array([False, False])
         tm.assert_numpy_array_equal(result, expected)
 
+    @pytest.mark.skip(reason="GH#20829 is reverted until after 0.24.0")
     def test_compare_custom_object(self):
-        """Make sure non supported operations on Timedelta returns NonImplemented
-        and yields to other operand (GH20829)."""
+        """
+        Make sure non supported operations on Timedelta returns NonImplemented
+        and yields to other operand (GH#20829).
+        """
         class CustomClass(object):
 
             def __init__(self, cmp_result=None):
@@ -139,11 +140,7 @@ def __gt__(self, other):
 
         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])
+    @pytest.mark.parametrize("val", ["string", 1])
     def test_compare_unknown_type(self, val):
         # GH20829
         t = Timedelta('1s')