Backport PR #36595: Partial Revert "ENH: infer freq in timedelta_range (#32377)" (#36659)

Co-authored-by: Simon Hawkins <simonjayhawkins@gmail.com>

Author: meeseeksmachine

doc/source/whatsnew/v1.1.3.rst

@@ -31,6 +31,7 @@ Fixed regressions
 ~~~~~~~~~~~~~~~~~
 - Fixed regression in :meth:`DataFrame.agg`, :meth:`DataFrame.apply`, :meth:`Series.agg`, and :meth:`Series.apply` where internal suffix is exposed to the users when no relabelling is applied (:issue:`36189`)
 - Fixed regression in :class:`IntegerArray` unary plus and minus operations raising a ``TypeError`` (:issue:`36063`)
+- Fixed regression when adding a :meth:`timedelta_range` to a :class:``Timestamp`` raised an ``ValueError`` (:issue:`35897`)
 - Fixed regression in :meth:`Series.__getitem__` incorrectly raising when the input was a tuple (:issue:`35534`)
 - Fixed regression in :meth:`Series.__getitem__` incorrectly raising when the input was a frozenset (:issue:`35747`)
 - Fixed regression in :meth:`read_excel` with ``engine="odf"`` caused ``UnboundLocalError`` in some cases where cells had nested child nodes (:issue:`36122`, :issue:`35802`)
@@ -62,7 +63,7 @@ Bug fixes
 
 Other
 ~~~~~
--
+- Reverted enhancement added in pandas-1.1.0 where :func:`timedelta_range` infers a frequency when passed ``start``, ``stop``, and ``periods`` (:issue:`32377`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/arrays/timedeltas.py

@@ -256,10 +256,6 @@ def _generate_range(cls, start, end, periods, freq, closed=None):
             index = generate_regular_range(start, end, periods, freq)
         else:
             index = np.linspace(start.value, end.value, periods).astype("i8")
-            if len(index) >= 2:
-                # Infer a frequency
-                td = Timedelta(index[1] - index[0])
-                freq = to_offset(td)
 
         if not left_closed:
             index = index[1:]

pandas/core/indexes/timedeltas.py

@@ -323,8 +323,8 @@ def timedelta_range(
 
     >>> pd.timedelta_range(start='1 day', end='5 days', periods=4)
     TimedeltaIndex(['1 days 00:00:00', '2 days 08:00:00', '3 days 16:00:00',
-                '5 days 00:00:00'],
-               dtype='timedelta64[ns]', freq='32H')
+                    '5 days 00:00:00'],
+                   dtype='timedelta64[ns]', freq=None)
     """
     if freq is None and com.any_none(periods, start, end):
         freq = "D"

pandas/tests/arithmetic/test_timedelta64.py

@@ -2119,3 +2119,20 @@ def test_td64arr_pow_invalid(self, scalar_td, box_with_array):
 
         with pytest.raises(TypeError, match=pattern):
             td1 ** scalar_td
+
+
+def test_add_timestamp_to_timedelta():
+    # GH: 35897
+    timestamp = pd.Timestamp.now()
+    result = timestamp + pd.timedelta_range("0s", "1s", periods=31)
+    expected = pd.DatetimeIndex(
+        [
+            timestamp
+            + (
+                pd.to_timedelta("0.033333333s") * i
+                + pd.to_timedelta("0.000000001s") * divmod(i, 3)[0]
+            )
+            for i in range(31)
+        ]
+    )
+    tm.assert_index_equal(result, expected)

pandas/tests/indexes/timedeltas/test_timedelta_range.py

@@ -38,7 +38,6 @@ def test_linspace_behavior(self, periods, freq):
         result = timedelta_range(start="0 days", end="4 days", periods=periods)
         expected = timedelta_range(start="0 days", end="4 days", freq=freq)
         tm.assert_index_equal(result, expected)
-        assert result.freq == freq
 
     def test_errors(self):
         # not enough params
@@ -79,3 +78,8 @@ def test_timedelta_range_freq_divide_end(self, start, end, freq, expected_period
         assert Timedelta(start) == res[0]
         assert Timedelta(end) >= res[-1]
         assert len(res) == expected_periods
+
+    def test_timedelta_range_infer_freq(self):
+        # https://github.com/pandas-dev/pandas/issues/35897
+        result = timedelta_range("0s", "1s", periods=31)
+        assert result.freq is None