BUG: partial-timestamp slicing near the end of year/quarter/month (#31064)

Author: jbrockmendel

doc/source/whatsnew/v1.1.0.rst

@@ -102,7 +102,7 @@ Interval
 
 Indexing
 ^^^^^^^^
-
+- Bug in slicing on a :class:`DatetimeIndex` with a partial-timestamp dropping high-resolution indices near the end of a year, quarter, or month (:issue:`31064`)
 -
 -
 

pandas/core/indexes/datetimes.py

@@ -5,7 +5,14 @@
 
 import numpy as np
 
-from pandas._libs import NaT, Timestamp, index as libindex, lib, tslib as libts
+from pandas._libs import (
+    NaT,
+    Timedelta,
+    Timestamp,
+    index as libindex,
+    lib,
+    tslib as libts,
+)
 from pandas._libs.tslibs import ccalendar, fields, parsing, timezones
 from pandas.util._decorators import Appender, Substitution, cache_readonly
 
@@ -31,7 +38,7 @@
 import pandas.core.tools.datetimes as tools
 
 from pandas.tseries.frequencies import Resolution, to_offset
-from pandas.tseries.offsets import Nano, prefix_mapping
+from pandas.tseries.offsets import prefix_mapping
 
 
 def _new_DatetimeIndex(cls, d):
@@ -519,27 +526,27 @@ def _parsed_string_to_bounds(self, reso, parsed):
             raise KeyError
         if reso == "year":
             start = Timestamp(parsed.year, 1, 1)
-            end = Timestamp(parsed.year, 12, 31, 23, 59, 59, 999999)
+            end = Timestamp(parsed.year + 1, 1, 1) - Timedelta(nanoseconds=1)
         elif reso == "month":
             d = ccalendar.get_days_in_month(parsed.year, parsed.month)
             start = Timestamp(parsed.year, parsed.month, 1)
-            end = Timestamp(parsed.year, parsed.month, d, 23, 59, 59, 999999)
+            end = start + Timedelta(days=d, nanoseconds=-1)
         elif reso == "quarter":
             qe = (((parsed.month - 1) + 2) % 12) + 1  # two months ahead
             d = ccalendar.get_days_in_month(parsed.year, qe)  # at end of month
             start = Timestamp(parsed.year, parsed.month, 1)
-            end = Timestamp(parsed.year, qe, d, 23, 59, 59, 999999)
+            end = Timestamp(parsed.year, qe, 1) + Timedelta(days=d, nanoseconds=-1)
         elif reso == "day":
             start = Timestamp(parsed.year, parsed.month, parsed.day)
-            end = start + timedelta(days=1) - Nano(1)
+            end = start + Timedelta(days=1, nanoseconds=-1)
         elif reso == "hour":
             start = Timestamp(parsed.year, parsed.month, parsed.day, parsed.hour)
-            end = start + timedelta(hours=1) - Nano(1)
+            end = start + Timedelta(hours=1, nanoseconds=-1)
         elif reso == "minute":
             start = Timestamp(
                 parsed.year, parsed.month, parsed.day, parsed.hour, parsed.minute
             )
-            end = start + timedelta(minutes=1) - Nano(1)
+            end = start + Timedelta(minutes=1, nanoseconds=-1)
         elif reso == "second":
             start = Timestamp(
                 parsed.year,
@@ -549,7 +556,7 @@ def _parsed_string_to_bounds(self, reso, parsed):
                 parsed.minute,
                 parsed.second,
             )
-            end = start + timedelta(seconds=1) - Nano(1)
+            end = start + Timedelta(seconds=1, nanoseconds=-1)
         elif reso == "microsecond":
             start = Timestamp(
                 parsed.year,
@@ -560,7 +567,7 @@ def _parsed_string_to_bounds(self, reso, parsed):
                 parsed.second,
                 parsed.microsecond,
             )
-            end = start + timedelta(microseconds=1) - Nano(1)
+            end = start + Timedelta(microseconds=1, nanoseconds=-1)
         # GH 24076
         # If an incoming date string contained a UTC offset, need to localize
         # the parsed date to this offset first before aligning with the index's

pandas/tests/indexes/datetimes/test_partial_slicing.py

@@ -142,6 +142,26 @@ def test_slice_year(self):
         expected = slice(3288, 3653)
         assert result == expected
 
+    @pytest.mark.parametrize(
+        "partial_dtime",
+        [
+            "2019",
+            "2019Q4",
+            "Dec 2019",
+            "2019-12-31",
+            "2019-12-31 23",
+            "2019-12-31 23:59",
+        ],
+    )
+    def test_slice_end_of_period_resolution(self, partial_dtime):
+        # GH#31064
+        dti = date_range("2019-12-31 23:59:55.999999999", periods=10, freq="s")
+
+        ser = pd.Series(range(10), index=dti)
+        result = ser[partial_dtime]
+        expected = ser.iloc[:5]
+        tm.assert_series_equal(result, expected)
+
     def test_slice_quarter(self):
         dti = date_range(freq="D", start=datetime(2000, 6, 1), periods=500)