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.venv/Lib/site-packages/pandas/tests/tseries/offsets/test_dst.py

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+"""
+Tests for DateOffset additions over Daylight Savings Time
+"""
+from datetime import timedelta
+
+import pytest
+import pytz
+
+from pandas._libs.tslibs import Timestamp
+from pandas._libs.tslibs.offsets import (
+    BMonthBegin,
+    BMonthEnd,
+    BQuarterBegin,
+    BQuarterEnd,
+    BYearBegin,
+    BYearEnd,
+    CBMonthBegin,
+    CBMonthEnd,
+    CustomBusinessDay,
+    DateOffset,
+    Day,
+    MonthBegin,
+    MonthEnd,
+    QuarterBegin,
+    QuarterEnd,
+    SemiMonthBegin,
+    SemiMonthEnd,
+    Week,
+    YearBegin,
+    YearEnd,
+)
+
+from pandas.tests.tseries.offsets.test_offsets import get_utc_offset_hours
+
+
+class TestDST:
+
+    # one microsecond before the DST transition
+    ts_pre_fallback = "2013-11-03 01:59:59.999999"
+    ts_pre_springfwd = "2013-03-10 01:59:59.999999"
+
+    # test both basic names and dateutil timezones
+    timezone_utc_offsets = {
+        "US/Eastern": {"utc_offset_daylight": -4, "utc_offset_standard": -5},
+        "dateutil/US/Pacific": {"utc_offset_daylight": -7, "utc_offset_standard": -8},
+    }
+    valid_date_offsets_singular = [
+        "weekday",
+        "day",
+        "hour",
+        "minute",
+        "second",
+        "microsecond",
+    ]
+    valid_date_offsets_plural = [
+        "weeks",
+        "days",
+        "hours",
+        "minutes",
+        "seconds",
+        "milliseconds",
+        "microseconds",
+    ]
+
+    def _test_all_offsets(self, n, **kwds):
+        valid_offsets = (
+            self.valid_date_offsets_plural
+            if n > 1
+            else self.valid_date_offsets_singular
+        )
+
+        for name in valid_offsets:
+            self._test_offset(offset_name=name, offset_n=n, **kwds)
+
+    def _test_offset(self, offset_name, offset_n, tstart, expected_utc_offset):
+        offset = DateOffset(**{offset_name: offset_n})
+
+        t = tstart + offset
+        if expected_utc_offset is not None:
+            assert get_utc_offset_hours(t) == expected_utc_offset
+
+        if offset_name == "weeks":
+            # dates should match
+            assert t.date() == timedelta(days=7 * offset.kwds["weeks"]) + tstart.date()
+            # expect the same day of week, hour of day, minute, second, ...
+            assert (
+                t.dayofweek == tstart.dayofweek
+                and t.hour == tstart.hour
+                and t.minute == tstart.minute
+                and t.second == tstart.second
+            )
+        elif offset_name == "days":
+            # dates should match
+            assert timedelta(offset.kwds["days"]) + tstart.date() == t.date()
+            # expect the same hour of day, minute, second, ...
+            assert (
+                t.hour == tstart.hour
+                and t.minute == tstart.minute
+                and t.second == tstart.second
+            )
+        elif offset_name in self.valid_date_offsets_singular:
+            # expect the singular offset value to match between tstart and t
+            datepart_offset = getattr(
+                t, offset_name if offset_name != "weekday" else "dayofweek"
+            )
+            assert datepart_offset == offset.kwds[offset_name]
+        else:
+            # the offset should be the same as if it was done in UTC
+            assert t == (tstart.tz_convert("UTC") + offset).tz_convert("US/Pacific")
+
+    def _make_timestamp(self, string, hrs_offset, tz):
+        if hrs_offset >= 0:
+            offset_string = f"{hrs_offset:02d}00"
+        else:
+            offset_string = f"-{(hrs_offset * -1):02}00"
+        return Timestamp(string + offset_string).tz_convert(tz)
+
+    def test_springforward_plural(self):
+        # test moving from standard to daylight savings
+        for tz, utc_offsets in self.timezone_utc_offsets.items():
+            hrs_pre = utc_offsets["utc_offset_standard"]
+            hrs_post = utc_offsets["utc_offset_daylight"]
+            self._test_all_offsets(
+                n=3,
+                tstart=self._make_timestamp(self.ts_pre_springfwd, hrs_pre, tz),
+                expected_utc_offset=hrs_post,
+            )
+
+    def test_fallback_singular(self):
+        # in the case of singular offsets, we don't necessarily know which utc
+        # offset the new Timestamp will wind up in (the tz for 1 month may be
+        # different from 1 second) so we don't specify an expected_utc_offset
+        for tz, utc_offsets in self.timezone_utc_offsets.items():
+            hrs_pre = utc_offsets["utc_offset_standard"]
+            self._test_all_offsets(
+                n=1,
+                tstart=self._make_timestamp(self.ts_pre_fallback, hrs_pre, tz),
+                expected_utc_offset=None,
+            )
+
+    def test_springforward_singular(self):
+        for tz, utc_offsets in self.timezone_utc_offsets.items():
+            hrs_pre = utc_offsets["utc_offset_standard"]
+            self._test_all_offsets(
+                n=1,
+                tstart=self._make_timestamp(self.ts_pre_springfwd, hrs_pre, tz),
+                expected_utc_offset=None,
+            )
+
+    offset_classes = {
+        MonthBegin: ["11/2/2012", "12/1/2012"],
+        MonthEnd: ["11/2/2012", "11/30/2012"],
+        BMonthBegin: ["11/2/2012", "12/3/2012"],
+        BMonthEnd: ["11/2/2012", "11/30/2012"],
+        CBMonthBegin: ["11/2/2012", "12/3/2012"],
+        CBMonthEnd: ["11/2/2012", "11/30/2012"],
+        SemiMonthBegin: ["11/2/2012", "11/15/2012"],
+        SemiMonthEnd: ["11/2/2012", "11/15/2012"],
+        Week: ["11/2/2012", "11/9/2012"],
+        YearBegin: ["11/2/2012", "1/1/2013"],
+        YearEnd: ["11/2/2012", "12/31/2012"],
+        BYearBegin: ["11/2/2012", "1/1/2013"],
+        BYearEnd: ["11/2/2012", "12/31/2012"],
+        QuarterBegin: ["11/2/2012", "12/1/2012"],
+        QuarterEnd: ["11/2/2012", "12/31/2012"],
+        BQuarterBegin: ["11/2/2012", "12/3/2012"],
+        BQuarterEnd: ["11/2/2012", "12/31/2012"],
+        Day: ["11/4/2012", "11/4/2012 23:00"],
+    }.items()
+
+    @pytest.mark.parametrize("tup", offset_classes)
+    def test_all_offset_classes(self, tup):
+        offset, test_values = tup
+
+        first = Timestamp(test_values[0], tz="US/Eastern") + offset()
+        second = Timestamp(test_values[1], tz="US/Eastern")
+        assert first == second
+
+
+@pytest.mark.parametrize(
+    "original_dt, target_dt, offset, tz",
+    [
+        pytest.param(
+            Timestamp("1900-01-01"),
+            Timestamp("1905-07-01"),
+            MonthBegin(66),
+            "Africa/Kinshasa",
+            marks=pytest.mark.xfail(
+                # error: Module has no attribute "__version__"
+                float(pytz.__version__) <= 2020.1,  # type: ignore[attr-defined]
+                reason="GH#41906",
+            ),
+        ),
+        (
+            Timestamp("2021-10-01 01:15"),
+            Timestamp("2021-10-31 01:15"),
+            MonthEnd(1),
+            "Europe/London",
+        ),
+        (
+            Timestamp("2010-12-05 02:59"),
+            Timestamp("2010-10-31 02:59"),
+            SemiMonthEnd(-3),
+            "Europe/Paris",
+        ),
+        (
+            Timestamp("2021-10-31 01:20"),
+            Timestamp("2021-11-07 01:20"),
+            CustomBusinessDay(2, weekmask="Sun Mon"),
+            "US/Eastern",
+        ),
+        (
+            Timestamp("2020-04-03 01:30"),
+            Timestamp("2020-11-01 01:30"),
+            YearBegin(1, month=11),
+            "America/Chicago",
+        ),
+    ],
+)
+def test_nontick_offset_with_ambiguous_time_error(original_dt, target_dt, offset, tz):
+    # .apply for non-Tick offsets throws AmbiguousTimeError when the target dt
+    # is dst-ambiguous
+    localized_dt = original_dt.tz_localize(tz)
+
+    msg = f"Cannot infer dst time from {target_dt}, try using the 'ambiguous' argument"
+    with pytest.raises(pytz.AmbiguousTimeError, match=msg):
+        localized_dt + offset