BUG: pandas Timestamp tz_localize and tz_convert do not preserve freq attribute (#25247)

Author: charlesdong1991

doc/source/whatsnew/v0.25.0.rst

@@ -95,7 +95,7 @@ Timezones
 ^^^^^^^^^
 
 - Bug in :func:`to_datetime` with ``utc=True`` and datetime strings that would apply previously parsed UTC offsets to subsequent arguments (:issue:`24992`)
--
+- Bug in :func:`Timestamp.tz_localize` and :func:`Timestamp.tz_convert` does not propagate ``freq`` (:issue:`25241`)
 -
 
 Numeric

pandas/_libs/tslibs/timestamps.pyx

@@ -1187,12 +1187,12 @@ class Timestamp(_Timestamp):
             value = tz_localize_to_utc(np.array([self.value], dtype='i8'), tz,
                                        ambiguous=ambiguous,
                                        nonexistent=nonexistent)[0]
-            return Timestamp(value, tz=tz)
+            return Timestamp(value, tz=tz, freq=self.freq)
         else:
             if tz is None:
                 # reset tz
                 value = tz_convert_single(self.value, UTC, self.tz)
-                return Timestamp(value, tz=None)
+                return Timestamp(value, tz=tz, freq=self.freq)
             else:
                 raise TypeError('Cannot localize tz-aware Timestamp, use '
                                 'tz_convert for conversions')
@@ -1222,7 +1222,7 @@ class Timestamp(_Timestamp):
                             'tz_localize to localize')
         else:
             # Same UTC timestamp, different time zone
-            return Timestamp(self.value, tz=tz)
+            return Timestamp(self.value, tz=tz, freq=self.freq)
 
     astimezone = tz_convert
 

pandas/tests/indexes/datetimes/test_timezones.py

@@ -825,6 +825,13 @@ def test_dti_drop_dont_lose_tz(self):
 
         assert ind.tz is not None
 
+    def test_dti_tz_conversion_freq(self, tz_naive_fixture):
+        # GH25241
+        t3 = DatetimeIndex(['2019-01-01 10:00'], freq='H')
+        assert t3.tz_localize(tz=tz_naive_fixture).freq == t3.freq
+        t4 = DatetimeIndex(['2019-01-02 12:00'], tz='UTC', freq='T')
+        assert t4.tz_convert(tz='UTC').freq == t4.freq
+
     def test_drop_dst_boundary(self):
         # see gh-18031
         tz = "Europe/Brussels"

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -780,6 +780,13 @@ def test_hash_equivalent(self):
         stamp = Timestamp(datetime(2011, 1, 1))
         assert d[stamp] == 5
 
+    def test_tz_conversion_freq(self, tz_naive_fixture):
+        # GH25241
+        t1 = Timestamp('2019-01-01 10:00', freq='H')
+        assert t1.tz_localize(tz=tz_naive_fixture).freq == t1.freq
+        t2 = Timestamp('2019-01-02 12:00', tz='UTC', freq='T')
+        assert t2.tz_convert(tz='UTC').freq == t2.freq
+
 
 class TestTimestampNsOperations(object):
 

pandas/tests/series/indexing/test_indexing.py

@@ -114,7 +114,8 @@ def test_getitem_get(test_data):
 
     # missing
     d = test_data.ts.index[0] - BDay()
-    with pytest.raises(KeyError, match=r"Timestamp\('1999-12-31 00:00:00'\)"):
+    msg = r"Timestamp\('1999-12-31 00:00:00', freq='B'\)"
+    with pytest.raises(KeyError, match=msg):
         test_data.ts[d]
 
     # None