From 5cf8073bd7248bd3b8553478a8885c117ad0abc6 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Sun, 18 Nov 2018 18:24:52 -0800
Subject: [PATCH 01/19] Add more timezone fixtures

---
 pandas/_libs/tslibs/conversion.pyx               | 8 ++++++--
 pandas/_libs/tslibs/timezones.pyx                | 2 +-
 pandas/conftest.py                               | 9 +++++----
 pandas/tests/indexes/datetimes/test_timezones.py | 5 +----
 pandas/tests/indexes/datetimes/test_tools.py     | 8 ++++----
 pandas/tests/scalar/timestamp/test_timezones.py  | 6 ++----
 6 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index c2897e1d0e8c8..5a33f91ffca5a 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -785,7 +785,8 @@ cdef inline int64_t[:] _tz_convert_one_way(int64_t[:] vals, object tz,
         Py_ssize_t i, n = len(vals)
         int64_t val
 
-    if get_timezone(tz) != 'UTC':
+    if not is_utc(get_timezone(tz)):
+    #if get_timezone(tz) != 'UTC':
         converted = np.empty(n, dtype=np.int64)
         if is_tzlocal(tz):
             for i in range(n):
@@ -890,7 +891,10 @@ def tz_localize_to_utc(ndarray[int64_t] vals, object tz, object ambiguous=None,
     if is_tzlocal(tz):
         for i in range(n):
             v = vals[i]
-            result[i] = _tz_convert_tzlocal_utc(v, tz, to_utc=True)
+            if v == NPY_NAT:
+                result[i] = NPY_NAT
+            else:
+                result[i] = _tz_convert_tzlocal_utc(v, tz, to_utc=True)
         return result
 
     if is_string_object(ambiguous):
diff --git a/pandas/_libs/tslibs/timezones.pyx b/pandas/_libs/tslibs/timezones.pyx
index a2a40a8aa1ca4..5fa8a45af3083 100644
--- a/pandas/_libs/tslibs/timezones.pyx
+++ b/pandas/_libs/tslibs/timezones.pyx
@@ -58,7 +58,7 @@ cpdef inline object get_timezone(object tz):
     UJSON/pytables. maybe_get_tz (below) is the inverse of this process.
     """
     if is_utc(tz):
-        return 'UTC'
+        return tz
     else:
         if treat_tz_as_dateutil(tz):
             if '.tar.gz' in tz._filename:
diff --git a/pandas/conftest.py b/pandas/conftest.py
index 479471332a274..50bf2cf342fa3 100644
--- a/pandas/conftest.py
+++ b/pandas/conftest.py
@@ -1,12 +1,12 @@
 import importlib
 import os
 
-from dateutil.tz import tzutc
+from dateutil.tz import tzutc, tzlocal
 import hypothesis
 from hypothesis import strategies as st
 import numpy as np
 import pytest
-from pytz import utc
+from pytz import utc, FixedOffset
 
 from pandas.compat import PY3
 import pandas.util._test_decorators as td
@@ -245,7 +245,7 @@ def datetime_tz_utc():
     return timezone.utc
 
 
-utc_objs = ['utc', utc, tzutc()]
+utc_objs = ['utc', 'dateutil/UTC', utc, tzutc()]
 if PY3:
     from datetime import timezone
     utc_objs.append(timezone.utc)
@@ -354,7 +354,8 @@ def unique_nulls_fixture(request):
 
 
 TIMEZONES = [None, 'UTC', 'US/Eastern', 'Asia/Tokyo', 'dateutil/US/Pacific',
-             'dateutil/Asia/Singapore']
+             'dateutil/Asia/Singapore', tzutc(), tzlocal(), FixedOffset(300),
+             FixedOffset(0)]
 
 
 @td.parametrize_fixture_doc(str(TIMEZONES))
diff --git a/pandas/tests/indexes/datetimes/test_timezones.py b/pandas/tests/indexes/datetimes/test_timezones.py
index 9ad540b174438..52f4f3c309038 100644
--- a/pandas/tests/indexes/datetimes/test_timezones.py
+++ b/pandas/tests/indexes/datetimes/test_timezones.py
@@ -774,10 +774,7 @@ def test_time_accessor(self, dtype):
 
     def test_timetz_accessor(self, tz_naive_fixture):
         # GH21358
-        if tz_naive_fixture is not None:
-            tz = dateutil.tz.gettz(tz_naive_fixture)
-        else:
-            tz = None
+        tz = timezones.maybe_get_tz(tz_naive_fixture)
 
         expected = np.array([time(10, 20, 30, tzinfo=tz), pd.NaT])
 
diff --git a/pandas/tests/indexes/datetimes/test_tools.py b/pandas/tests/indexes/datetimes/test_tools.py
index c24c1025ea63c..e31d63ff8c3b9 100644
--- a/pandas/tests/indexes/datetimes/test_tools.py
+++ b/pandas/tests/indexes/datetimes/test_tools.py
@@ -409,8 +409,8 @@ def test_to_datetime_tz_pytz(self, cache):
                                                      hour=3, minute=0))],
                        dtype=object)
         result = pd.to_datetime(arr, utc=True, cache=cache)
-        expected = DatetimeIndex(['2000-01-01 08:00:00+00:00',
-                                  '2000-06-01 07:00:00+00:00'],
+        expected = DatetimeIndex(['2000-01-01 08:00:00',
+                                  '2000-06-01 07:00:00'],
                                  dtype='datetime64[ns, UTC]', freq=None)
         tm.assert_index_equal(result, expected)
 
@@ -488,8 +488,8 @@ def test_to_datetime_tz_psycopg2(self, cache):
                        dtype=object)
 
         result = pd.to_datetime(arr, errors='coerce', utc=True, cache=cache)
-        expected = DatetimeIndex(['2000-01-01 08:00:00+00:00',
-                                  '2000-06-01 07:00:00+00:00'],
+        expected = DatetimeIndex(['2000-01-01 08:00:00',
+                                  '2000-06-01 07:00:00'],
                                  dtype='datetime64[ns, UTC]', freq=None)
         tm.assert_index_equal(result, expected)
 
diff --git a/pandas/tests/scalar/timestamp/test_timezones.py b/pandas/tests/scalar/timestamp/test_timezones.py
index 6755d0bd4ae27..a859c081877b0 100644
--- a/pandas/tests/scalar/timestamp/test_timezones.py
+++ b/pandas/tests/scalar/timestamp/test_timezones.py
@@ -11,6 +11,7 @@
 import dateutil
 from dateutil.tz import gettz, tzoffset
 
+from pandas._libs.tslibs import timezones
 import pandas.util.testing as tm
 import pandas.util._test_decorators as td
 
@@ -342,10 +343,7 @@ def test_timestamp_add_timedelta_push_over_dst_boundary(self, tz):
     def test_timestamp_timetz_equivalent_with_datetime_tz(self,
                                                           tz_naive_fixture):
         # GH21358
-        if tz_naive_fixture is not None:
-            tz = dateutil.tz.gettz(tz_naive_fixture)
-        else:
-            tz = None
+        tz = timezones.maybe_get_tz(tz_naive_fixture)
 
         stamp = Timestamp('2018-06-04 10:20:30', tz=tz)
         _datetime = datetime(2018, 6, 4, hour=10,

From 7ba3649e542d9e175c105b3cffb79a0cbd879ee9 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Sun, 18 Nov 2018 18:46:11 -0800
Subject: [PATCH 02/19] convert 'UTC' to UTC const

---
 pandas/_libs/tslib.pyx                          |  5 +++--
 pandas/_libs/tslibs/conversion.pyx              | 15 +++++++--------
 pandas/_libs/tslibs/offsets.pyx                 |  3 ++-
 pandas/_libs/tslibs/timestamps.pyx              |  9 +++++----
 pandas/tests/scalar/timestamp/test_timestamp.py |  2 +-
 5 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/pandas/_libs/tslib.pyx b/pandas/_libs/tslib.pyx
index e346eb7e598ed..c5bc969ede3c9 100644
--- a/pandas/_libs/tslib.pyx
+++ b/pandas/_libs/tslib.pyx
@@ -33,6 +33,7 @@ from tslibs.parsing import parse_datetime_string
 
 from tslibs.timedeltas cimport cast_from_unit
 from tslibs.timezones cimport is_utc, is_tzlocal, get_dst_info
+from tslibs.timezones import UTC
 from tslibs.conversion cimport (tz_convert_single, _TSObject,
                                 convert_datetime_to_tsobject,
                                 get_datetime64_nanos,
@@ -211,7 +212,7 @@ def _test_parse_iso8601(object ts):
     check_dts_bounds(&obj.dts)
     if out_local == 1:
         obj.tzinfo = pytz.FixedOffset(out_tzoffset)
-        obj.value = tz_convert_single(obj.value, obj.tzinfo, 'UTC')
+        obj.value = tz_convert_single(obj.value, obj.tzinfo, UTC)
         return Timestamp(obj.value, tz=obj.tzinfo)
     else:
         return Timestamp(obj.value)
@@ -673,7 +674,7 @@ cpdef array_to_datetime(ndarray[object] values, errors='raise',
                         # dateutil.tz.tzoffset objects
                         out_tzoffset_vals.add(out_tzoffset * 60.)
                         tz = pytz.FixedOffset(out_tzoffset)
-                        value = tz_convert_single(value, tz, 'UTC')
+                        value = tz_convert_single(value, tz, UTC)
                     else:
                         # Add a marker for naive string, to track if we are
                         # parsing mixed naive and aware strings
diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index 5a33f91ffca5a..925c30e8f4aa8 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -35,6 +35,7 @@ from timedeltas cimport cast_from_unit
 from timezones cimport (is_utc, is_tzlocal, is_fixed_offset,
                         get_utcoffset, get_dst_info,
                         get_timezone, maybe_get_tz, tz_compare)
+from timezones import UTC
 from parsing import parse_datetime_string
 
 from nattype import nat_strings, NaT
@@ -46,8 +47,6 @@ from nattype cimport NPY_NAT, checknull_with_nat
 NS_DTYPE = np.dtype('M8[ns]')
 TD_DTYPE = np.dtype('m8[ns]')
 
-UTC = pytz.UTC
-
 
 # ----------------------------------------------------------------------
 # Misc Helpers
@@ -442,7 +441,7 @@ cdef _TSObject convert_str_to_tsobject(object ts, object tz, object unit,
             check_dts_bounds(&obj.dts)
             if out_local == 1:
                 obj.tzinfo = pytz.FixedOffset(out_tzoffset)
-                obj.value = tz_convert_single(obj.value, obj.tzinfo, 'UTC')
+                obj.value = tz_convert_single(obj.value, obj.tzinfo, UTC)
                 if tz is None:
                     check_dts_bounds(&obj.dts)
                     check_overflows(obj)
@@ -576,7 +575,7 @@ cdef inline datetime _localize_pydatetime(datetime dt, tzinfo tz):
         identically, i.e. discards nanos from Timestamps.
         It also assumes that the `tz` input is not None.
     """
-    if tz == 'UTC' or tz is UTC:
+    if is_utc(tz):
         return UTC.localize(dt)
     try:
         # datetime.replace with pytz may be incorrect result
@@ -603,7 +602,7 @@ cpdef inline datetime localize_pydatetime(datetime dt, object tz):
     elif not PyDateTime_CheckExact(dt):
         # i.e. is a Timestamp
         return dt.tz_localize(tz)
-    elif tz == 'UTC' or tz is UTC:
+    elif is_utc(tz):
         return UTC.localize(dt)
     try:
         # datetime.replace with pytz may be incorrect result
@@ -735,7 +734,7 @@ cpdef int64_t tz_convert_single(int64_t val, object tz1, object tz2):
         int64_t arr[1]
 
     # See GH#17734 We should always be converting either from UTC or to UTC
-    assert (is_utc(tz1) or tz1 == 'UTC') or (is_utc(tz2) or tz2 == 'UTC')
+    assert is_utc(tz1) or is_utc(tz2)
 
     if val == NPY_NAT:
         return val
@@ -743,13 +742,13 @@ cpdef int64_t tz_convert_single(int64_t val, object tz1, object tz2):
     # Convert to UTC
     if is_tzlocal(tz1):
         utc_date = _tz_convert_tzlocal_utc(val, tz1, to_utc=True)
-    elif get_timezone(tz1) != 'UTC':
+    elif not is_utc(get_timezone(tz1)):
         arr[0] = val
         utc_date = _tz_convert_dst(arr, tz1, to_utc=True)[0]
     else:
         utc_date = val
 
-    if get_timezone(tz2) == 'UTC':
+    if is_utc(get_timezone(tz2)):
         return utc_date
     elif is_tzlocal(tz2):
         return _tz_convert_tzlocal_utc(utc_date, tz2, to_utc=False)
diff --git a/pandas/_libs/tslibs/offsets.pyx b/pandas/_libs/tslibs/offsets.pyx
index 7ef38cba0c37f..f3ac102bf177e 100644
--- a/pandas/_libs/tslibs/offsets.pyx
+++ b/pandas/_libs/tslibs/offsets.pyx
@@ -26,6 +26,7 @@ from conversion cimport tz_convert_single, pydt_to_i8, localize_pydatetime
 from nattype cimport NPY_NAT
 from np_datetime cimport (npy_datetimestruct,
                           dtstruct_to_dt64, dt64_to_dtstruct)
+from timezones import UTC
 
 # ---------------------------------------------------------------------
 # Constants
@@ -211,7 +212,7 @@ def _to_dt64(dt, dtype='datetime64'):
     # Thus astype is needed to cast datetime to datetime64[D]
     if getattr(dt, 'tzinfo', None) is not None:
         i8 = pydt_to_i8(dt)
-        dt = tz_convert_single(i8, 'UTC', dt.tzinfo)
+        dt = tz_convert_single(i8, UTC, dt.tzinfo)
         dt = np.int64(dt).astype('datetime64[ns]')
     else:
         dt = np.datetime64(dt)
diff --git a/pandas/_libs/tslibs/timestamps.pyx b/pandas/_libs/tslibs/timestamps.pyx
index f6a6257f92e7c..bb7a9a57b8a75 100644
--- a/pandas/_libs/tslibs/timestamps.pyx
+++ b/pandas/_libs/tslibs/timestamps.pyx
@@ -36,6 +36,7 @@ from timedeltas import Timedelta
 from timedeltas cimport delta_to_nanoseconds
 from timezones cimport (
     get_timezone, is_utc, maybe_get_tz, treat_tz_as_pytz, tz_compare)
+from timezones import UTC
 
 # ----------------------------------------------------------------------
 # Constants
@@ -416,7 +417,7 @@ cdef class _Timestamp(datetime):
             int64_t val
         val = self.value
         if self.tz is not None and not is_utc(self.tz):
-            val = tz_convert_single(self.value, 'UTC', self.tz)
+            val = tz_convert_single(self.value, UTC, self.tz)
         return val
 
     cpdef bint _get_start_end_field(self, str field):
@@ -633,7 +634,7 @@ class Timestamp(_Timestamp):
 
         Return a new Timestamp representing UTC day and time.
         """
-        return cls.now('UTC')
+        return cls.now(UTC)
 
     @classmethod
     def utcfromtimestamp(cls, ts):
@@ -1108,7 +1109,7 @@ class Timestamp(_Timestamp):
         else:
             if tz is None:
                 # reset tz
-                value = tz_convert_single(self.value, 'UTC', self.tz)
+                value = tz_convert_single(self.value, UTC, self.tz)
                 return Timestamp(value, tz=None)
             else:
                 raise TypeError('Cannot localize tz-aware Timestamp, use '
@@ -1178,7 +1179,7 @@ class Timestamp(_Timestamp):
         _tzinfo = self.tzinfo
         value = self.value
         if _tzinfo is not None:
-            value_tz = tz_convert_single(value, _tzinfo, 'UTC')
+            value_tz = tz_convert_single(value, _tzinfo, UTC)
             value += value - value_tz
 
         # setup components
diff --git a/pandas/tests/scalar/timestamp/test_timestamp.py b/pandas/tests/scalar/timestamp/test_timestamp.py
index c1f532d56304c..0d1e63f910dcf 100644
--- a/pandas/tests/scalar/timestamp/test_timestamp.py
+++ b/pandas/tests/scalar/timestamp/test_timestamp.py
@@ -613,7 +613,7 @@ def test_tz(self):
         assert conv.hour == 19
 
     def test_utc_z_designator(self):
-        assert get_timezone(Timestamp('2014-11-02 01:00Z').tzinfo) == 'UTC'
+        assert get_timezone(Timestamp('2014-11-02 01:00Z').tzinfo) is utc
 
     def test_asm8(self):
         np.random.seed(7960929)

From 5662f3a7aac56a72a56c8be54367b04a40ebdb78 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Sun, 18 Nov 2018 19:22:38 -0800
Subject: [PATCH 03/19] Fix more occurances of 'UTC'

---
 pandas/_libs/tslibs/conversion.pyx | 7 ++++++-
 pandas/core/arrays/datetimes.py    | 3 ++-
 pandas/tseries/frequencies.py      | 3 ++-
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index cee064abb113e..0446378fc6da2 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -641,7 +641,10 @@ cdef inline int64_t[:] _tz_convert_dst(int64_t[:] values, tzinfo tz,
         int64_t[:] deltas
         int64_t v
 
-    trans, deltas, typ = get_dst_info(tz)
+    if not is_tzlocal(tz):
+        # get_dst_info cannot extract offsets from tzlocal because its
+        # dependent on a datetime
+        trans, deltas, typ = get_dst_info(tz)
     if not to_utc:
         # We add `offset` below instead of subtracting it
         deltas = -1 * np.array(deltas, dtype='i8')
@@ -650,6 +653,8 @@ cdef inline int64_t[:] _tz_convert_dst(int64_t[:] values, tzinfo tz,
         v = values[i]
         if v == NPY_NAT:
             result[i] = v
+        elif is_tzlocal(tz):
+            result[i] = _tz_convert_tzlocal_utc(v, tz, to_utc=to_utc)
         else:
             # TODO: Is it more efficient to call searchsorted pointwise or
             # on `values` outside the loop?  We are not consistent about this.
diff --git a/pandas/core/arrays/datetimes.py b/pandas/core/arrays/datetimes.py
index c56e994e0ca2f..27ecf97cc1e62 100644
--- a/pandas/core/arrays/datetimes.py
+++ b/pandas/core/arrays/datetimes.py
@@ -797,7 +797,8 @@ def tz_localize(self, tz, ambiguous='raise', nonexistent='raise',
 
         if self.tz is not None:
             if tz is None:
-                new_dates = conversion.tz_convert(self.asi8, 'UTC', self.tz)
+                new_dates = conversion.tz_convert(self.asi8, timezones.UTC,
+                                                  self.tz)
             else:
                 raise TypeError("Already tz-aware, use tz_convert to convert.")
         else:
diff --git a/pandas/tseries/frequencies.py b/pandas/tseries/frequencies.py
index ac9a87b258056..62603db80489c 100644
--- a/pandas/tseries/frequencies.py
+++ b/pandas/tseries/frequencies.py
@@ -30,6 +30,7 @@
 from pandas._libs.tslibs.resolution import Resolution
 from pandas._libs.tslibs.fields import build_field_sarray
 from pandas._libs.tslibs.conversion import tz_convert
+from pandas._libs.tslibs.timezones import UTC
 
 from pandas._libs.algos import unique_deltas
 
@@ -298,7 +299,7 @@ def __init__(self, index, warn=True):
         # the timezone so they are in local time
         if hasattr(index, 'tz'):
             if index.tz is not None:
-                self.values = tz_convert(self.values, 'UTC', index.tz)
+                self.values = tz_convert(self.values, UTC, index.tz)
 
         self.warn = warn
 

From 28030419947f68892e1f87020e0e7734db1e49f7 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Sun, 18 Nov 2018 20:52:28 -0800
Subject: [PATCH 04/19] Add notes

---
 pandas/_libs/tslibs/conversion.pyx | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index 0446378fc6da2..86e0dcb275972 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -692,6 +692,7 @@ cdef inline int64_t _tz_convert_tzlocal_utc(int64_t val, tzinfo tz,
         datetime dt
 
     dt64_to_dtstruct(val, &dts)
+    # THIS NEEDS TO BE A LOCAL DATETIME!
     dt = datetime(dts.year, dts.month, dts.day, dts.hour,
                   dts.min, dts.sec, dts.us, tz)
     delta = int(get_utcoffset(tz, dt).total_seconds()) * 1000000000
@@ -790,7 +791,6 @@ cdef inline int64_t[:] _tz_convert_one_way(int64_t[:] vals, object tz,
         int64_t val
 
     if not is_utc(get_timezone(tz)):
-    #if get_timezone(tz) != 'UTC':
         converted = np.empty(n, dtype=np.int64)
         if is_tzlocal(tz):
             for i in range(n):

From c5e11a62299f091b854587d8a3ab18c5da70a509 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Sun, 18 Nov 2018 23:03:43 -0800
Subject: [PATCH 05/19] fix tzlocal with iteration

---
 pandas/_libs/tslibs/conversion.pyx | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index 86e0dcb275972..2835e36b4f0e4 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -8,6 +8,7 @@ from numpy cimport int64_t, int32_t, ndarray
 cnp.import_array()
 
 import pytz
+from dateutil.tz import tzutc
 
 # stdlib datetime imports
 from datetime import time as datetime_time
@@ -539,7 +540,8 @@ cdef inline void localize_tso(_TSObject obj, tzinfo tz):
     elif obj.value == NPY_NAT:
         pass
     elif is_tzlocal(tz):
-        local_val = _tz_convert_tzlocal_utc(obj.value, tz, to_utc=False)
+        local_val = _tz_convert_tzlocal_utc(obj.value, tz, to_utc=False,
+                                            from_utc=True)
         dt64_to_dtstruct(local_val, &obj.dts)
     else:
         # Adjust datetime64 timestamp, recompute datetimestruct
@@ -668,7 +670,8 @@ cdef inline int64_t[:] _tz_convert_dst(int64_t[:] values, tzinfo tz,
 
 
 cdef inline int64_t _tz_convert_tzlocal_utc(int64_t val, tzinfo tz,
-                                            bint to_utc=True):
+                                            bint to_utc=True,
+                                            bint from_utc=False):
     """
     Convert the i8 representation of a datetime from a tzlocal timezone to
     UTC, or vice-versa.
@@ -681,6 +684,8 @@ cdef inline int64_t _tz_convert_tzlocal_utc(int64_t val, tzinfo tz,
     tz : tzinfo
     to_utc : bint
         True if converting tzlocal _to_ UTC, False if going the other direction
+    from_utc: bint
+        True if val is a UTC timestamp, False if val is a wall/naive timestamp
 
     Returns
     -------
@@ -693,8 +698,12 @@ cdef inline int64_t _tz_convert_tzlocal_utc(int64_t val, tzinfo tz,
 
     dt64_to_dtstruct(val, &dts)
     # THIS NEEDS TO BE A LOCAL DATETIME!
+    # get_utcoffset (utcoffset udh) assumes the datetime is a wall time
     dt = datetime(dts.year, dts.month, dts.day, dts.hour,
-                  dts.min, dts.sec, dts.us, tz)
+                  dts.min, dts.sec, dts.us)
+    if from_utc:
+        dt = dt.replace(tzinfo=tzutc())
+        dt = dt.astimezone(tz)
     delta = int(get_utcoffset(tz, dt).total_seconds()) * 1000000000
 
     if not to_utc:
@@ -713,7 +722,7 @@ cdef inline int64_t tz_convert_utc_to_tzlocal(int64_t utc_val, tzinfo tz):
     -------
     local_val : int64_t
     """
-    return _tz_convert_tzlocal_utc(utc_val, tz, to_utc=False)
+    return _tz_convert_tzlocal_utc(utc_val, tz, to_utc=False, from_utc=True)
 
 
 cpdef int64_t tz_convert_single(int64_t val, object tz1, object tz2):

From fbc50da50f421d4ddcdb85ee85bf04e78562325d Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Sun, 18 Nov 2018 23:26:07 -0800
Subject: [PATCH 06/19] move codeblock

---
 pandas/_libs/tslibs/conversion.pyx | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index 2835e36b4f0e4..2d8394078415f 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -647,9 +647,9 @@ cdef inline int64_t[:] _tz_convert_dst(int64_t[:] values, tzinfo tz,
         # get_dst_info cannot extract offsets from tzlocal because its
         # dependent on a datetime
         trans, deltas, typ = get_dst_info(tz)
-    if not to_utc:
-        # We add `offset` below instead of subtracting it
-        deltas = -1 * np.array(deltas, dtype='i8')
+        if not to_utc:
+            # We add `offset` below instead of subtracting it
+            deltas = -1 * np.array(deltas, dtype='i8')
 
     for i in range(n):
         v = values[i]

From f351cd2e917432f800c1c91e8e692e8ff0280b4e Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Mon, 19 Nov 2018 21:10:46 -0800
Subject: [PATCH 07/19] fix tz_localize(None) tzlocal() for Timestamp

---
 pandas/_libs/tslibs/conversion.pyx | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index 2d8394078415f..b4ea1a625ef15 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -697,10 +697,10 @@ cdef inline int64_t _tz_convert_tzlocal_utc(int64_t val, tzinfo tz,
         datetime dt
 
     dt64_to_dtstruct(val, &dts)
-    # THIS NEEDS TO BE A LOCAL DATETIME!
-    # get_utcoffset (utcoffset udh) assumes the datetime is a wall time
     dt = datetime(dts.year, dts.month, dts.day, dts.hour,
                   dts.min, dts.sec, dts.us)
+    # get_utcoffset (tz.utcoffset under the hood) only makes sense if datetime
+    # is _wall time_, so if val is a UTC timestamp convert to wall time
     if from_utc:
         dt = dt.replace(tzinfo=tzutc())
         dt = dt.astimezone(tz)
@@ -766,7 +766,8 @@ cpdef int64_t tz_convert_single(int64_t val, object tz1, object tz2):
     if is_utc(get_timezone(tz2)):
         return utc_date
     elif is_tzlocal(tz2):
-        return _tz_convert_tzlocal_utc(utc_date, tz2, to_utc=False)
+        return _tz_convert_tzlocal_utc(utc_date, tz2, to_utc=False,
+                                       from_utc=True)
     else:
         # Convert UTC to other timezone
         arr[0] = utc_date

From 5b97f0dfaa4823e2e66183d65ebce39ed078d6ac Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Mon, 19 Nov 2018 21:22:36 -0800
Subject: [PATCH 08/19] Fix tz_localize(None) with tzlocal for DTI

---
 pandas/_libs/tslibs/conversion.pyx | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index b4ea1a625ef15..4c240e26e3100 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -781,7 +781,7 @@ cpdef int64_t tz_convert_single(int64_t val, object tz1, object tz2):
 @cython.boundscheck(False)
 @cython.wraparound(False)
 cdef inline int64_t[:] _tz_convert_one_way(int64_t[:] vals, object tz,
-                                           bint to_utc):
+                                           bint to_utc, bint from_utc=False):
     """
     Convert the given values (in i8) either to UTC or from UTC.
 
@@ -790,6 +790,9 @@ cdef inline int64_t[:] _tz_convert_one_way(int64_t[:] vals, object tz,
     vals : int64 ndarray
     tz1 : string / timezone object
     to_utc : bint
+    from_utc : bint
+        True if vals are UTC timestamps, False if vals are wall timestamps
+        Only applicable for tz=dateutil.tz.tzlocal()
 
     Returns
     -------
@@ -808,7 +811,8 @@ cdef inline int64_t[:] _tz_convert_one_way(int64_t[:] vals, object tz,
                 if val == NPY_NAT:
                     converted[i] = NPY_NAT
                 else:
-                    converted[i] = _tz_convert_tzlocal_utc(val, tz, to_utc)
+                    converted[i] = _tz_convert_tzlocal_utc(val, tz, to_utc,
+                                                           from_utc=from_utc)
         else:
             converted = _tz_convert_dst(vals, tz, to_utc)
     else:
@@ -841,7 +845,8 @@ def tz_convert(int64_t[:] vals, object tz1, object tz2):
 
     # Convert to UTC
     utc_dates = _tz_convert_one_way(vals, tz1, to_utc=True)
-    converted = _tz_convert_one_way(utc_dates, tz2, to_utc=False)
+    converted = _tz_convert_one_way(utc_dates, tz2, to_utc=False,
+                                    from_utc=True)
     return np.array(converted, dtype=np.int64)
 
 

From 81646883b8c40eb9f9e45a03b24854cd09d457a0 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Mon, 19 Nov 2018 21:47:37 -0800
Subject: [PATCH 09/19] Add test for tzlocal and NaT

---
 pandas/tests/indexes/datetimes/test_construction.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/pandas/tests/indexes/datetimes/test_construction.py b/pandas/tests/indexes/datetimes/test_construction.py
index 4b2c07af6af68..5c555b7c0ea66 100644
--- a/pandas/tests/indexes/datetimes/test_construction.py
+++ b/pandas/tests/indexes/datetimes/test_construction.py
@@ -5,6 +5,7 @@
 import numpy as np
 import pytest
 import pytz
+import dateutil
 
 from pandas._libs.tslib import OutOfBoundsDatetime
 from pandas._libs.tslibs import conversion
@@ -527,6 +528,12 @@ def test_construction_with_tz_and_tz_aware_dti(self):
         with pytest.raises(TypeError):
             DatetimeIndex(dti, tz='Asia/Tokyo')
 
+    def test_construction_with_nat_and_tzlocal(self):
+        tz = dateutil.tz.tzlocal()
+        result = DatetimeIndex(['2018', 'NaT'], tz=tz)
+        expected = DatetimeIndex([Timestamp('2018', tz=tz), pd.NaT])
+        tm.assert_index_equal(result, expected)
+
 
 class TestTimeSeries(object):
 

From 069e6e1c16a02e52b8ca106d607e814c8f5211e6 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Mon, 19 Nov 2018 21:57:38 -0800
Subject: [PATCH 10/19] Add whatsnew

---
 doc/source/whatsnew/v0.24.0.rst | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/doc/source/whatsnew/v0.24.0.rst b/doc/source/whatsnew/v0.24.0.rst
index 7d8ee975ba02c..c597dcee60e6d 100644
--- a/doc/source/whatsnew/v0.24.0.rst
+++ b/doc/source/whatsnew/v0.24.0.rst
@@ -1248,6 +1248,8 @@ Timezones
 - Bug when indexing a :class:`Series` with a DST transition (:issue:`21846`)
 - Bug in :meth:`DataFrame.resample` and :meth:`Series.resample` where an ``AmbiguousTimeError`` or ``NonExistentTimeError`` would raise if a timezone aware timeseries ended on a DST transition (:issue:`19375`, :issue:`10117`)
 - Bug in :meth:`DataFrame.drop` and :meth:`Series.drop` when specifying a tz-aware Timestamp key to drop from a :class:`DatetimeIndex` with a DST transition (:issue:`21761`)
+- Bug in :class:`DatetimeIndex` constructor where :class:`NaT` and ``dateutil.tz.tzlocal`` would raise an ``OutOfBoundsDatetime`` error (:issue:``)
+- Bug in :meth:`DatetimeIndex.tz_localize` and :meth:`Timestamp.tz_localize` with ``dateutil.tz.tzlocal`` near a DST transition that would return an incorrectly localized datetime (:issue:``)
 
 Offsets
 ^^^^^^^

From de3c83bb946a7791d29a18db5f004228b24c9b02 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Mon, 19 Nov 2018 22:10:41 -0800
Subject: [PATCH 11/19] Add issue number and one more fixedoffset

---
 doc/source/whatsnew/v0.24.0.rst | 4 ++--
 pandas/conftest.py              | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/doc/source/whatsnew/v0.24.0.rst b/doc/source/whatsnew/v0.24.0.rst
index c597dcee60e6d..cde8b176ba244 100644
--- a/doc/source/whatsnew/v0.24.0.rst
+++ b/doc/source/whatsnew/v0.24.0.rst
@@ -1248,8 +1248,8 @@ Timezones
 - Bug when indexing a :class:`Series` with a DST transition (:issue:`21846`)
 - Bug in :meth:`DataFrame.resample` and :meth:`Series.resample` where an ``AmbiguousTimeError`` or ``NonExistentTimeError`` would raise if a timezone aware timeseries ended on a DST transition (:issue:`19375`, :issue:`10117`)
 - Bug in :meth:`DataFrame.drop` and :meth:`Series.drop` when specifying a tz-aware Timestamp key to drop from a :class:`DatetimeIndex` with a DST transition (:issue:`21761`)
-- Bug in :class:`DatetimeIndex` constructor where :class:`NaT` and ``dateutil.tz.tzlocal`` would raise an ``OutOfBoundsDatetime`` error (:issue:``)
-- Bug in :meth:`DatetimeIndex.tz_localize` and :meth:`Timestamp.tz_localize` with ``dateutil.tz.tzlocal`` near a DST transition that would return an incorrectly localized datetime (:issue:``)
+- Bug in :class:`DatetimeIndex` constructor where :class:`NaT` and ``dateutil.tz.tzlocal`` would raise an ``OutOfBoundsDatetime`` error (:issue:`23807`)
+- Bug in :meth:`DatetimeIndex.tz_localize` and :meth:`Timestamp.tz_localize` with ``dateutil.tz.tzlocal`` near a DST transition that would return an incorrectly localized datetime (:issue:`23807`)
 
 Offsets
 ^^^^^^^
diff --git a/pandas/conftest.py b/pandas/conftest.py
index 50bf2cf342fa3..3810828f60190 100644
--- a/pandas/conftest.py
+++ b/pandas/conftest.py
@@ -355,7 +355,7 @@ def unique_nulls_fixture(request):
 
 TIMEZONES = [None, 'UTC', 'US/Eastern', 'Asia/Tokyo', 'dateutil/US/Pacific',
              'dateutil/Asia/Singapore', tzutc(), tzlocal(), FixedOffset(300),
-             FixedOffset(0)]
+             FixedOffset(0), FixedOffset(-300)]
 
 
 @td.parametrize_fixture_doc(str(TIMEZONES))

From fb6e96c566d655dc1abaa40dae81e3a6a53bb21d Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Tue, 20 Nov 2018 21:15:32 -0800
Subject: [PATCH 12/19] fix dateutil UTC converted to pytz UTC

---
 doc/source/whatsnew/v0.24.0.rst                 | 1 +
 pandas/_libs/tslibs/conversion.pyx              | 2 +-
 pandas/tests/scalar/timestamp/test_timestamp.py | 6 ++++++
 pandas/tests/tslibs/test_conversion.py          | 9 +++++----
 4 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/doc/source/whatsnew/v0.24.0.rst b/doc/source/whatsnew/v0.24.0.rst
index 0df95bee6d30a..0c52b4aed3d19 100644
--- a/doc/source/whatsnew/v0.24.0.rst
+++ b/doc/source/whatsnew/v0.24.0.rst
@@ -1251,6 +1251,7 @@ Timezones
 - Bug in :meth:`DataFrame.drop` and :meth:`Series.drop` when specifying a tz-aware Timestamp key to drop from a :class:`DatetimeIndex` with a DST transition (:issue:`21761`)
 - Bug in :class:`DatetimeIndex` constructor where :class:`NaT` and ``dateutil.tz.tzlocal`` would raise an ``OutOfBoundsDatetime`` error (:issue:`23807`)
 - Bug in :meth:`DatetimeIndex.tz_localize` and :meth:`Timestamp.tz_localize` with ``dateutil.tz.tzlocal`` near a DST transition that would return an incorrectly localized datetime (:issue:`23807`)
+- Bug in :class:`Timestamp` constructor where a ``dateutil.tz.tzutc`` timezone passed with a ``datetime.datetime`` argument would be converted to a ``pytz.UTC`` timezone (:issue:`23807`)
 
 Offsets
 ^^^^^^^
diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index 4c240e26e3100..f55f8cbd501d8 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -362,7 +362,7 @@ cdef _TSObject convert_datetime_to_tsobject(datetime ts, object tz,
         else:
             # UTC
             obj.value = pydatetime_to_dt64(ts, &obj.dts)
-            obj.tzinfo = pytz.utc
+            obj.tzinfo = tz
     else:
         obj.value = pydatetime_to_dt64(ts, &obj.dts)
         obj.tzinfo = ts.tzinfo
diff --git a/pandas/tests/scalar/timestamp/test_timestamp.py b/pandas/tests/scalar/timestamp/test_timestamp.py
index d24a79bfc63ca..8a834a45daf7c 100644
--- a/pandas/tests/scalar/timestamp/test_timestamp.py
+++ b/pandas/tests/scalar/timestamp/test_timestamp.py
@@ -589,6 +589,12 @@ def test_depreciate_tz_and_tzinfo_in_datetime_input(self, box):
         with tm.assert_produces_warning(FutureWarning):
             Timestamp(box(**kwargs), tz='US/Pacific')
 
+    def test_dont_convert_dateutil_utc_to_pytz_utc(self):
+        result = Timestamp(datetime(2018, 1, 1), tz=tzutc())
+        expected = Timestamp(datetime(2018, 1, 1)).tz_localize(tzutc())
+        assert result == expected
+        assert result.tz is tzutc()
+
 
 class TestTimestamp(object):
 
diff --git a/pandas/tests/tslibs/test_conversion.py b/pandas/tests/tslibs/test_conversion.py
index de36c0bb2f789..fde1d1718a2a2 100644
--- a/pandas/tests/tslibs/test_conversion.py
+++ b/pandas/tests/tslibs/test_conversion.py
@@ -2,6 +2,7 @@
 
 import numpy as np
 import pytest
+from pytz import UTC
 
 from pandas._libs.tslib import iNaT
 from pandas._libs.tslibs import conversion, timezones
@@ -11,15 +12,15 @@
 
 
 def compare_utc_to_local(tz_didx, utc_didx):
-    f = lambda x: conversion.tz_convert_single(x, 'UTC', tz_didx.tz)
-    result = conversion.tz_convert(tz_didx.asi8, 'UTC', tz_didx.tz)
+    f = lambda x: conversion.tz_convert_single(x, UTC, tz_didx.tz)
+    result = conversion.tz_convert(tz_didx.asi8, UTC, tz_didx.tz)
     result_single = np.vectorize(f)(tz_didx.asi8)
     tm.assert_numpy_array_equal(result, result_single)
 
 
 def compare_local_to_utc(tz_didx, utc_didx):
-    f = lambda x: conversion.tz_convert_single(x, tz_didx.tz, 'UTC')
-    result = conversion.tz_convert(utc_didx.asi8, tz_didx.tz, 'UTC')
+    f = lambda x: conversion.tz_convert_single(x, tz_didx.tz, UTC)
+    result = conversion.tz_convert(utc_didx.asi8, tz_didx.tz, UTC)
     result_single = np.vectorize(f)(utc_didx.asi8)
     tm.assert_numpy_array_equal(result, result_single)
 

From 555afaafe3ee7c269499faec1de50b9dd8a648e6 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Tue, 20 Nov 2018 22:00:53 -0800
Subject: [PATCH 13/19] Fix some tests

---
 pandas/tests/series/test_analytics.py | 2 +-
 pandas/tseries/offsets.py             | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/pandas/tests/series/test_analytics.py b/pandas/tests/series/test_analytics.py
index a5a7cc2217864..e01d91661c2e6 100644
--- a/pandas/tests/series/test_analytics.py
+++ b/pandas/tests/series/test_analytics.py
@@ -338,7 +338,7 @@ def test_describe(self):
     def test_describe_with_tz(self, tz_naive_fixture):
         # GH 21332
         tz = tz_naive_fixture
-        name = tz_naive_fixture
+        name = str(tz_naive_fixture)
         start = Timestamp(2018, 1, 1)
         end = Timestamp(2018, 1, 5)
         s = Series(date_range(start, end, tz=tz), name=name)
diff --git a/pandas/tseries/offsets.py b/pandas/tseries/offsets.py
index ca81b3bcfef2a..fedcf46277515 100644
--- a/pandas/tseries/offsets.py
+++ b/pandas/tseries/offsets.py
@@ -9,7 +9,7 @@
 from pandas._libs.tslibs import (
     NaT, OutOfBoundsDatetime, Timedelta, Timestamp, ccalendar, conversion,
     delta_to_nanoseconds, frequencies as libfrequencies, normalize_date,
-    offsets as liboffsets)
+    offsets as liboffsets, timezones)
 from pandas._libs.tslibs.offsets import (
     ApplyTypeError, BaseOffset, _get_calendar, _is_normalized, _to_dt64,
     apply_index_wraps, as_datetime, roll_yearday, shift_month)
@@ -81,7 +81,7 @@ def wrapper(self, other):
                     if result.tz is not None:
                         # convert to UTC
                         value = conversion.tz_convert_single(
-                            result.value, 'UTC', result.tz)
+                            result.value, timezones.UTC, result.tz)
                     else:
                         value = result.value
                     result = Timestamp(value + nano)

From 9857897c20e213549e8fb1fd1587339d147876c9 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Tue, 20 Nov 2018 23:27:24 -0800
Subject: [PATCH 14/19] don't assume pytz.UTC should localize a datetime

---
 pandas/_libs/tslibs/conversion.pyx | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index f55f8cbd501d8..9b3a63e6e972e 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -577,8 +577,6 @@ cdef inline datetime _localize_pydatetime(datetime dt, tzinfo tz):
         identically, i.e. discards nanos from Timestamps.
         It also assumes that the `tz` input is not None.
     """
-    if is_utc(tz):
-        return UTC.localize(dt)
     try:
         # datetime.replace with pytz may be incorrect result
         return tz.localize(dt)
@@ -605,7 +603,7 @@ cpdef inline datetime localize_pydatetime(datetime dt, object tz):
         # i.e. is a Timestamp
         return dt.tz_localize(tz)
     elif is_utc(tz):
-        return UTC.localize(dt)
+        return _localize_pydatetime(dt, tz)
     try:
         # datetime.replace with pytz may be incorrect result
         return tz.localize(dt)

From c647ba052ea245f719d94e7e5daa17ca1bce6e03 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Wed, 21 Nov 2018 10:24:07 -0800
Subject: [PATCH 15/19] isort

---
 pandas/conftest.py                                  | 8 ++++----
 pandas/tests/indexes/datetimes/test_construction.py | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/pandas/conftest.py b/pandas/conftest.py
index 3810828f60190..9c326c3d502d8 100644
--- a/pandas/conftest.py
+++ b/pandas/conftest.py
@@ -1,16 +1,16 @@
 import importlib
 import os
 
-from dateutil.tz import tzutc, tzlocal
-import hypothesis
-from hypothesis import strategies as st
+from dateutil.tz import tzlocal, tzutc
 import numpy as np
 import pytest
-from pytz import utc, FixedOffset
+from pytz import FixedOffset, utc
 
 from pandas.compat import PY3
 import pandas.util._test_decorators as td
 
+import hypothesis
+from hypothesis import strategies as st
 import pandas as pd
 
 hypothesis.settings.register_profile(
diff --git a/pandas/tests/indexes/datetimes/test_construction.py b/pandas/tests/indexes/datetimes/test_construction.py
index 5c555b7c0ea66..02755c7e58a1d 100644
--- a/pandas/tests/indexes/datetimes/test_construction.py
+++ b/pandas/tests/indexes/datetimes/test_construction.py
@@ -2,10 +2,10 @@
 from functools import partial
 from operator import attrgetter
 
+import dateutil
 import numpy as np
 import pytest
 import pytz
-import dateutil
 
 from pandas._libs.tslib import OutOfBoundsDatetime
 from pandas._libs.tslibs import conversion

From c219ea3ed0aeb3c1ca6661ce34cc5699d9977c5f Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Wed, 21 Nov 2018 11:18:35 -0800
Subject: [PATCH 16/19] extract actual timezone object for DatetimeTZDtype

---
 pandas/core/dtypes/dtypes.py                 | 4 ++--
 pandas/tests/indexes/datetimes/test_tools.py | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/pandas/core/dtypes/dtypes.py b/pandas/core/dtypes/dtypes.py
index 4dfefdec031b2..bd7c6630c7c5d 100644
--- a/pandas/core/dtypes/dtypes.py
+++ b/pandas/core/dtypes/dtypes.py
@@ -5,7 +5,7 @@
 import numpy as np
 
 from pandas._libs.interval import Interval
-from pandas._libs.tslibs import NaT, Period, Timestamp
+from pandas._libs.tslibs import NaT, Period, Timestamp, timezones
 
 from pandas.core.dtypes.generic import ABCCategoricalIndex, ABCIndexClass
 
@@ -516,7 +516,7 @@ def __new__(cls, unit=None, tz=None):
                 m = cls._match.search(unit)
                 if m is not None:
                     unit = m.groupdict()['unit']
-                    tz = m.groupdict()['tz']
+                    tz = timezones.maybe_get_tz(m.groupdict()['tz'])
             except TypeError:
                 raise ValueError("could not construct DatetimeTZDtype")
 
diff --git a/pandas/tests/indexes/datetimes/test_tools.py b/pandas/tests/indexes/datetimes/test_tools.py
index e31d63ff8c3b9..c24c1025ea63c 100644
--- a/pandas/tests/indexes/datetimes/test_tools.py
+++ b/pandas/tests/indexes/datetimes/test_tools.py
@@ -409,8 +409,8 @@ def test_to_datetime_tz_pytz(self, cache):
                                                      hour=3, minute=0))],
                        dtype=object)
         result = pd.to_datetime(arr, utc=True, cache=cache)
-        expected = DatetimeIndex(['2000-01-01 08:00:00',
-                                  '2000-06-01 07:00:00'],
+        expected = DatetimeIndex(['2000-01-01 08:00:00+00:00',
+                                  '2000-06-01 07:00:00+00:00'],
                                  dtype='datetime64[ns, UTC]', freq=None)
         tm.assert_index_equal(result, expected)
 
@@ -488,8 +488,8 @@ def test_to_datetime_tz_psycopg2(self, cache):
                        dtype=object)
 
         result = pd.to_datetime(arr, errors='coerce', utc=True, cache=cache)
-        expected = DatetimeIndex(['2000-01-01 08:00:00',
-                                  '2000-06-01 07:00:00'],
+        expected = DatetimeIndex(['2000-01-01 08:00:00+00:00',
+                                  '2000-06-01 07:00:00+00:00'],
                                  dtype='datetime64[ns, UTC]', freq=None)
         tm.assert_index_equal(result, expected)
 

From 44a33ab2471ff838c14026f87c4acab2c54fcd1e Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Wed, 21 Nov 2018 11:37:23 -0800
Subject: [PATCH 17/19] from_utc -> not to_utc

---
 pandas/_libs/tslibs/conversion.pyx | 26 ++++++++------------------
 1 file changed, 8 insertions(+), 18 deletions(-)

diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index 9b3a63e6e972e..b4a13d3d0ada9 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -540,8 +540,7 @@ cdef inline void localize_tso(_TSObject obj, tzinfo tz):
     elif obj.value == NPY_NAT:
         pass
     elif is_tzlocal(tz):
-        local_val = _tz_convert_tzlocal_utc(obj.value, tz, to_utc=False,
-                                            from_utc=True)
+        local_val = _tz_convert_tzlocal_utc(obj.value, tz, to_utc=False)
         dt64_to_dtstruct(local_val, &obj.dts)
     else:
         # Adjust datetime64 timestamp, recompute datetimestruct
@@ -668,8 +667,7 @@ cdef inline int64_t[:] _tz_convert_dst(int64_t[:] values, tzinfo tz,
 
 
 cdef inline int64_t _tz_convert_tzlocal_utc(int64_t val, tzinfo tz,
-                                            bint to_utc=True,
-                                            bint from_utc=False):
+                                            bint to_utc=True):
     """
     Convert the i8 representation of a datetime from a tzlocal timezone to
     UTC, or vice-versa.
@@ -682,8 +680,6 @@ cdef inline int64_t _tz_convert_tzlocal_utc(int64_t val, tzinfo tz,
     tz : tzinfo
     to_utc : bint
         True if converting tzlocal _to_ UTC, False if going the other direction
-    from_utc: bint
-        True if val is a UTC timestamp, False if val is a wall/naive timestamp
 
     Returns
     -------
@@ -699,7 +695,7 @@ cdef inline int64_t _tz_convert_tzlocal_utc(int64_t val, tzinfo tz,
                   dts.min, dts.sec, dts.us)
     # get_utcoffset (tz.utcoffset under the hood) only makes sense if datetime
     # is _wall time_, so if val is a UTC timestamp convert to wall time
-    if from_utc:
+    if not to_utc:
         dt = dt.replace(tzinfo=tzutc())
         dt = dt.astimezone(tz)
     delta = int(get_utcoffset(tz, dt).total_seconds()) * 1000000000
@@ -720,7 +716,7 @@ cdef inline int64_t tz_convert_utc_to_tzlocal(int64_t utc_val, tzinfo tz):
     -------
     local_val : int64_t
     """
-    return _tz_convert_tzlocal_utc(utc_val, tz, to_utc=False, from_utc=True)
+    return _tz_convert_tzlocal_utc(utc_val, tz, to_utc=False)
 
 
 cpdef int64_t tz_convert_single(int64_t val, object tz1, object tz2):
@@ -764,8 +760,7 @@ cpdef int64_t tz_convert_single(int64_t val, object tz1, object tz2):
     if is_utc(get_timezone(tz2)):
         return utc_date
     elif is_tzlocal(tz2):
-        return _tz_convert_tzlocal_utc(utc_date, tz2, to_utc=False,
-                                       from_utc=True)
+        return _tz_convert_tzlocal_utc(utc_date, tz2, to_utc=False)
     else:
         # Convert UTC to other timezone
         arr[0] = utc_date
@@ -779,7 +774,7 @@ cpdef int64_t tz_convert_single(int64_t val, object tz1, object tz2):
 @cython.boundscheck(False)
 @cython.wraparound(False)
 cdef inline int64_t[:] _tz_convert_one_way(int64_t[:] vals, object tz,
-                                           bint to_utc, bint from_utc=False):
+                                           bint to_utc):
     """
     Convert the given values (in i8) either to UTC or from UTC.
 
@@ -788,9 +783,6 @@ cdef inline int64_t[:] _tz_convert_one_way(int64_t[:] vals, object tz,
     vals : int64 ndarray
     tz1 : string / timezone object
     to_utc : bint
-    from_utc : bint
-        True if vals are UTC timestamps, False if vals are wall timestamps
-        Only applicable for tz=dateutil.tz.tzlocal()
 
     Returns
     -------
@@ -809,8 +801,7 @@ cdef inline int64_t[:] _tz_convert_one_way(int64_t[:] vals, object tz,
                 if val == NPY_NAT:
                     converted[i] = NPY_NAT
                 else:
-                    converted[i] = _tz_convert_tzlocal_utc(val, tz, to_utc,
-                                                           from_utc=from_utc)
+                    converted[i] = _tz_convert_tzlocal_utc(val, tz, to_utc)
         else:
             converted = _tz_convert_dst(vals, tz, to_utc)
     else:
@@ -843,8 +834,7 @@ def tz_convert(int64_t[:] vals, object tz1, object tz2):
 
     # Convert to UTC
     utc_dates = _tz_convert_one_way(vals, tz1, to_utc=True)
-    converted = _tz_convert_one_way(utc_dates, tz2, to_utc=False,
-                                    from_utc=True)
+    converted = _tz_convert_one_way(utc_dates, tz2, to_utc=False)
     return np.array(converted, dtype=np.int64)
 
 

From 9828aa502e15d110bc88af050bfe484ecfa5c20b Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Wed, 21 Nov 2018 12:35:42 -0800
Subject: [PATCH 18/19] Assert already checks timezone

---
 pandas/tests/scalar/timestamp/test_timestamp.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/pandas/tests/scalar/timestamp/test_timestamp.py b/pandas/tests/scalar/timestamp/test_timestamp.py
index 8a834a45daf7c..b2c05d1564a48 100644
--- a/pandas/tests/scalar/timestamp/test_timestamp.py
+++ b/pandas/tests/scalar/timestamp/test_timestamp.py
@@ -593,7 +593,6 @@ def test_dont_convert_dateutil_utc_to_pytz_utc(self):
         result = Timestamp(datetime(2018, 1, 1), tz=tzutc())
         expected = Timestamp(datetime(2018, 1, 1)).tz_localize(tzutc())
         assert result == expected
-        assert result.tz is tzutc()
 
 
 class TestTimestamp(object):

From 15ba5fb8bb462672d2153e2b4e0db4146a2a58d9 Mon Sep 17 00:00:00 2001
From: Matt Roeschke <mroeschke@housecanary.com>
Date: Wed, 21 Nov 2018 18:48:27 -0800
Subject: [PATCH 19/19] isort

---
 pandas/conftest.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/conftest.py b/pandas/conftest.py
index 9c326c3d502d8..f450193d9388e 100644
--- a/pandas/conftest.py
+++ b/pandas/conftest.py
@@ -2,6 +2,8 @@
 import os
 
 from dateutil.tz import tzlocal, tzutc
+import hypothesis
+from hypothesis import strategies as st
 import numpy as np
 import pytest
 from pytz import FixedOffset, utc
@@ -9,8 +11,6 @@
 from pandas.compat import PY3
 import pandas.util._test_decorators as td
 
-import hypothesis
-from hypothesis import strategies as st
 import pandas as pd
 
 hypothesis.settings.register_profile(