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BUG: DatetimeIndex.astype matches Series.dtype with datetime tz dtype #33409

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BUG: DatetimeIndex.astype matches Series.dtype with datetime tz dtype #33409

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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v1.1.0.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -400,7 +400,7 @@ Timezones
^^^^^^^^^

- Bug in :func:`to_datetime` with ``infer_datetime_format=True`` where timezone names (e.g. ``UTC``) would not be parsed correctly (:issue:`33133`)
-
- Bug in :func:`DatetimeIndex.astype` with a ``datetime64[ns, tz]`` dtype where the data was not localized to UTC first (:issue:`33401`)


Numeric
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3 changes: 2 additions & 1 deletion pandas/core/arrays/datetimes.py
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Expand Up @@ -586,7 +586,8 @@ def astype(self, dtype, copy=True):
# GH#18951: datetime64_ns dtype but not equal means different tz
new_tz = getattr(dtype, "tz", None)
if getattr(self.dtype, "tz", None) is None:
return self.tz_localize(new_tz)
# GH 33401: Match the behavior of Series.astype
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is it obvious that Series is the better behavior? it might be that the only unambiguous thing to do is raise and require the user to be explicit

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That's fair. The implicit UTC localization isn't my favorite behavior.

With that in mind, should we deprecate the Series.astype(tz_dtype) UTC localization behavior instead?

return self.tz_localize(timezones.UTC).tz_convert(new_tz)
result = self.tz_convert(new_tz)
if copy:
result = result.copy()
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17 changes: 16 additions & 1 deletion pandas/tests/indexes/datetimes/test_astype.py
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Expand Up @@ -90,9 +90,14 @@ def test_astype_with_tz(self):
tm.assert_index_equal(result, expected)

# GH 18951: tz-naive to tz-aware
# GH 33401: Match the behavior of Series.astype
idx = date_range("20170101", periods=4)
result = idx.astype("datetime64[ns, US/Eastern]")
expected = date_range("20170101", periods=4, tz="US/Eastern")
expected = (
date_range("20170101", periods=4)
.tz_localize("UTC")
.tz_convert("US/Eastern")
)
tm.assert_index_equal(result, expected)

def test_astype_str_compat(self):
Expand Down Expand Up @@ -321,3 +326,13 @@ def test_astype_array_fallback(self, tz):
result = obj._data.astype(bool)
expected = np.array([True, True])
tm.assert_numpy_array_equal(result, expected)

def test_astype_tz_dtype_utc_localization(self):
# GH 33401
result = pd.Index([pd.Timestamp("2020-01-01 15:00")]).astype(
"datetime64[ns, US/Eastern]"
)
expected = pd.Index([pd.Timestamp("2020-01-01 10:00")]).tz_localize(
"US/Eastern"
)
tm.assert_index_equal(result, expected)