Add whatsnew and more comments

pandas-dev · jreback · Jun 13, 2018 · Jun 9, 2018 · Jun 9, 2018 · Jun 10, 2018
commit f4eb827790f356dec7a7e382ee0642126a2403ed
diff --git a/doc/source/whatsnew/v0.23.1.txt b/doc/source/whatsnew/v0.23.1.txt
@@ -129,6 +129,10 @@ Bug Fixes
 - Bug in :func:`concat` where error was raised in concatenating :class:`Series` with numpy scalar and tuple names (:issue:`21015`)
 - Bug in :func:`concat` warning message providing the wrong guidance for future behavior (:issue:`21101`)
 
+**Timezones**
+- Bug in :class:`Timestamp` and :class:`DatetimeIndex` where passing a :class:`Timestamp` localized after a DST transition would return a datetime before the DST transition (:issue:`20854`)
+- Bug in comparing :class:`DataFrame`s with tz-aware :class:`DatetimeIndex` columns with a DST transition that raised a ``KeyError`` (:issue:`19970`)
+
 **Other**
 
 - Tab completion on :class:`Index` in IPython no longer outputs deprecation warnings (:issue:`21125`)

diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
@@ -1,6 +1,8 @@
 # -*- coding: utf-8 -*-
 # cython: profile=False
 
+from warnings import catch_warnings
+
 cimport cython
 from cython cimport Py_ssize_t
 
@@ -347,13 +349,14 @@ cdef _TSObject convert_datetime_to_tsobject(datetime ts, object tz,
     if tz is not None:
         tz = maybe_get_tz(tz)
 
-        # sort of a temporary hack
         if ts.tzinfo is not None:
             if hasattr(tz, 'normalize') and hasattr(ts.tzinfo, '_utcoffset'):
                 # tz.localize does not correctly localize Timestamps near DST
+                # but correctly localizes datetimes
                 if hasattr(ts, 'to_pydatetime'):
                     nanos += ts.nanosecond
-                    ts = ts.to_pydatetime()
+                    with catch_warnings(record=True):
+                        ts = ts.to_pydatetime()
                 ts = tz.normalize(ts)
                 obj.value = pydatetime_to_dt64(ts, &obj.dts)
                 obj.tzinfo = ts.tzinfo