BUG: Timestamp.tz_localize resets nanosecond

doc/source/v0.14.1.txt

@@ -248,7 +248,7 @@ Bug Fixes
 
 - BUG in ``resample`` raises ``ValueError`` when target contains ``NaT`` (:issue:`7227`)
 
-
+- Bug in ``Timestamp.tz_convert`` resets ``nanosecond`` info (:issue:`7534`)
 
 - Bug in ``Index.astype(float)`` where it would return an ``object`` dtype
   ``Index`` (:issue:`7464`).

pandas/tseries/tests/test_timezones.py

@@ -1,5 +1,5 @@
 # pylint: disable-msg=E1101,W0612
-from datetime import datetime, time, timedelta, tzinfo, date
+from datetime import datetime, timedelta, tzinfo, date
 import sys
 import os
 import unittest
@@ -8,10 +8,9 @@
 import numpy as np
 import pytz
 
-from pandas import (Index, Series, TimeSeries, DataFrame, isnull,
-                    date_range, Timestamp)
+from pandas import (Index, Series, DataFrame, isnull, Timestamp)
 
-from pandas import DatetimeIndex, Int64Index, to_datetime, NaT
+from pandas import DatetimeIndex, to_datetime, NaT
 from pandas import tslib
 
 import pandas.core.datetools as datetools
@@ -20,17 +19,10 @@
 import pandas.tseries.tools as tools
 from pytz import NonExistentTimeError
 
-from pandas.util.testing import assert_series_equal, assert_almost_equal, assertRaisesRegexp
 import pandas.util.testing as tm
 
-import pandas.lib as lib
-import pandas.core.datetools as dt
-from numpy.random import rand
 from pandas.util.testing import assert_frame_equal
-import pandas.compat as compat
-from pandas.compat import range, lrange, zip, cPickle as pickle
-from pandas.core.datetools import BDay
-import pandas.core.common as com
+from pandas.compat import lrange, zip
 
 from pandas import _np_version_under1p7
 
@@ -544,13 +536,13 @@ def test_localized_at_time_between_time(self):
 
         result = ts_local.at_time(time(10, 0))
         expected = ts.at_time(time(10, 0)).tz_localize(self.tzstr('US/Eastern'))
-        assert_series_equal(result, expected)
+        tm.assert_series_equal(result, expected)
         self.assertTrue(self.cmptz(result.index.tz, self.tz('US/Eastern')))
 
         t1, t2 = time(10, 0), time(11, 0)
         result = ts_local.between_time(t1, t2)
         expected = ts.between_time(t1, t2).tz_localize(self.tzstr('US/Eastern'))
-        assert_series_equal(result, expected)
+        tm.assert_series_equal(result, expected)
         self.assertTrue(self.cmptz(result.index.tz, self.tz('US/Eastern')))
 
     def test_string_index_alias_tz_aware(self):
@@ -631,7 +623,7 @@ def test_frame_no_datetime64_dtype(self):
                         'datetimes_with_tz' : datetimes_with_tz })
         result = df.get_dtype_counts()
         expected = Series({ 'datetime64[ns]' : 3, 'object' : 1 })
-        assert_series_equal(result, expected)
+        tm.assert_series_equal(result, expected)
 
     def test_hongkong_tz_convert(self):
         # #1673
@@ -863,7 +855,7 @@ def test_series_frame_tz_localize(self):
         # Can't localize if already tz-aware
         rng = date_range('1/1/2011', periods=100, freq='H', tz='utc')
         ts = Series(1, index=rng)
-        assertRaisesRegexp(TypeError, 'Already tz-aware', ts.tz_localize, 'US/Eastern')
+        tm.assertRaisesRegexp(TypeError, 'Already tz-aware', ts.tz_localize, 'US/Eastern')
 
     def test_series_frame_tz_convert(self):
         rng = date_range('1/1/2011', periods=200, freq='D',
@@ -887,7 +879,7 @@ def test_series_frame_tz_convert(self):
         # can't convert tz-naive
         rng = date_range('1/1/2011', periods=200, freq='D')
         ts = Series(1, index=rng)
-        assertRaisesRegexp(TypeError, "Cannot convert tz-naive", ts.tz_convert, 'US/Eastern')
+        tm.assertRaisesRegexp(TypeError, "Cannot convert tz-naive", ts.tz_convert, 'US/Eastern')
 
     def test_join_utc_convert(self):
         rng = date_range('1/1/2011', periods=100, freq='H', tz='utc')
@@ -1033,7 +1025,7 @@ def test_arith_utc_convert(self):
         expected = uts1 + uts2
 
         self.assertEqual(result.index.tz, pytz.UTC)
-        assert_series_equal(result, expected)
+        tm.assert_series_equal(result, expected)
 
     def test_intersection(self):
         rng = date_range('1/1/2011', periods=100, freq='H', tz='utc')

pandas/tseries/tests/test_tslib.py

@@ -9,6 +9,7 @@
 from pandas.tslib import period_asfreq, period_ordinal
 from pandas.tseries.index import date_range
 from pandas.tseries.frequencies import get_freq
+import pandas.tseries.offsets as offsets
 from pandas import _np_version_under1p7
 import pandas.util.testing as tm
 from pandas.util.testing import assert_series_equal
@@ -61,7 +62,7 @@ def test_bounds_with_different_units(self):
             for unit in time_units:
                 self.assertRaises(
                     ValueError,
-                    tslib.Timestamp,
+                    Timestamp,
                     np.datetime64(date_string, dtype='M8[%s]' % unit)
                 )
 
@@ -72,27 +73,48 @@ def test_bounds_with_different_units(self):
 
         for date_string in in_bounds_dates:
             for unit in time_units:
-                tslib.Timestamp(
+                Timestamp(
                     np.datetime64(date_string, dtype='M8[%s]' % unit)
                 )
 
+    def test_tz(self):
+        t = '2014-02-01 09:00'
+        ts = Timestamp(t)
+        local = ts.tz_localize('Asia/Tokyo')
+        self.assertEqual(local.hour, 9)
+        self.assertEqual(local, Timestamp(t, tz='Asia/Tokyo'))
+        conv = local.tz_convert('US/Eastern')
+        self.assertEqual(conv,
+                         Timestamp('2014-01-31 19:00', tz='US/Eastern'))
+        self.assertEqual(conv.hour, 19)
+
+        # preserves nanosecond
+        ts = Timestamp(t) + offsets.Nano(5)
+        local = ts.tz_localize('Asia/Tokyo')
+        self.assertEqual(local.hour, 9)
+        self.assertEqual(local.nanosecond, 5)
+        conv = local.tz_convert('US/Eastern')
+        self.assertEqual(conv.nanosecond, 5)
+        self.assertEqual(conv.hour, 19)
+
     def test_barely_oob_dts(self):
         one_us = np.timedelta64(1)
 
         # By definition we can't go out of bounds in [ns], so we
         # convert the datetime64s to [us] so we can go out of bounds
-        min_ts_us = np.datetime64(tslib.Timestamp.min).astype('M8[us]')
-        max_ts_us = np.datetime64(tslib.Timestamp.max).astype('M8[us]')
+        min_ts_us = np.datetime64(Timestamp.min).astype('M8[us]')
+        max_ts_us = np.datetime64(Timestamp.max).astype('M8[us]')
 
         # No error for the min/max datetimes
-        tslib.Timestamp(min_ts_us)
-        tslib.Timestamp(max_ts_us)
+        Timestamp(min_ts_us)
+        Timestamp(max_ts_us)
 
         # One us less than the minimum is an error
-        self.assertRaises(ValueError, tslib.Timestamp, min_ts_us - one_us)
+        self.assertRaises(ValueError, Timestamp, min_ts_us - one_us)
 
         # One us more than the maximum is an error
-        self.assertRaises(ValueError, tslib.Timestamp, max_ts_us + one_us)
+        self.assertRaises(ValueError, Timestamp, max_ts_us + one_us)
+
 
 class TestDatetimeParsingWrappers(tm.TestCase):
     def test_does_not_convert_mixed_integer(self):

pandas/tslib.pyx

@@ -341,21 +341,26 @@ class Timestamp(_Timestamp):
     def is_year_end(self):
         return self._get_start_end_field('is_year_end')
 
-    def tz_localize(self, tz):
+    def tz_localize(self, tz, infer_dst=False):
         """
         Convert naive Timestamp to local time zone
 
         Parameters
         ----------
         tz : pytz.timezone or dateutil.tz.tzfile
+        infer_dst : boolean, default False
+            Attempt to infer fall dst-transition hours based on order
 
         Returns
         -------
         localized : Timestamp
         """
         if self.tzinfo is None:
             # tz naive, localize
-            return Timestamp(self.to_pydatetime(), tz=tz)
+            tz = maybe_get_tz(tz)
+            value = tz_localize_to_utc(np.array([self.value]), tz,
+                                       infer_dst=infer_dst)[0]
+            return Timestamp(value, tz=tz)
         else:
             raise Exception('Cannot localize tz-aware Timestamp, use '
                             'tz_convert for conversions')