Expand tests for pandas-dev#17965 to various datetimelikes

Author: watercrossing

doc/source/whatsnew/v0.21.1.txt

@@ -61,7 +61,7 @@ Bug Fixes
 - Bug in :class:`DatetimeIndex` subtracting datetimelike from DatetimeIndex could fail to overflow (:issue:`18020`)
 - Bug in ``pd.Series.rolling.skew()`` and ``rolling.kurt()`` with all equal values has floating issue (:issue:`18044`)
 - Bug in ``pd.DataFrameGroupBy.count()`` when counting over a datetimelike column (:issue:`13393`)
-- Bug in ``_libs.index.convert_scalar()`` when comparing datetimes to np.datetime64 (:issue:`17965`)
+- Bug in ``_libs.index.convert_scalar()``: Comparison between ``datetime64[ns]`` series and ``datetimelike`` (:issue:`17965`)
 
 Conversion
 ^^^^^^^^^^

pandas/_libs/src/datetime/np_datetime_strings.c

@@ -509,12 +509,14 @@ int parse_iso_8601_datetime(char *str, int len, PANDAS_DATETIMEUNIT unit,
 
     /* Skip leading whitespace */
     while (sublen > 0 && isspace(*substr)) {
+		PyErr_Warn(PyExc_Warning, "leading whitespace skipped");
         ++substr;
         --sublen;
     }
 
     /* Leading '-' sign for negative year */
     if (*substr == '-') {
+		PyErr_Warn(PyExc_Warning, "leading negative sign");
         ++substr;
         --sublen;
     }

pandas/tests/indexes/datetimes/test_partial_slicing.py

@@ -5,6 +5,8 @@
 from datetime import datetime
 import numpy as np
 import pandas as pd
+from itertools import product
+import operator as op
 
 from pandas import (DatetimeIndex, Series, DataFrame,
                     date_range, Index, Timedelta, Timestamp)
@@ -331,8 +333,22 @@ def test_loc_datetime_length_one(self):
         result = df.loc['2016-10-01T00:00:00':]
         tm.assert_frame_equal(result, df)
 
-    def test_comparison_to_datetime64(self):
-        # GH issue #17965
-        df = DataFrame({'dates': date_range('2000-01-01', '2000-01-05')})
-        date = df['dates'].unique()[0]
-        tm.assert_frame_equal(df.loc[df['dates'] == date], df.iloc[:1])
+    comparisonTS = Timestamp('20130101')
+
+    @pytest.mark.parametrize('datetimelike,opExp', product(
+        [comparisonTS, comparisonTS.to_pydatetime(),
+         comparisonTS.to_pydatetime().date(), comparisonTS.to_datetime64()],
+        [(op.lt, [True, False, False, False]),
+         (op.le, [True, True, False, False]),
+         (op.eq, [False, True, False, False]),
+         (op.gt, [False, False, False, True])]))
+    def test_selection_by_datetimelike(self, datetimelike, opExp):
+        # GH issue #17965, test for ability to compare datetime64[ns] columns
+        # to datetimelike
+        op, exp = opExp
+        df = DataFrame({'A': [pd.Timestamp('20120101'),
+                              pd.Timestamp('20130101'),
+                              np.nan, pd.Timestamp('20130103')]})
+        result = op(df.A, datetimelike)
+        expected = Series(exp, name='A')
+        tm.assert_series_equal(result, expected)