From 03dd25e4e89c8be0a914cf4fb10eebbae57de897 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Wed, 1 Jul 2020 09:30:21 -0700
Subject: [PATCH 1/2] CLN: require to_utc or from_utc in tz_convert

---
 pandas/_libs/tslibs/tzconversion.pyx   | 45 +++++++++++++-------------
 pandas/tests/tslibs/test_conversion.py |  7 ++--
 2 files changed, 27 insertions(+), 25 deletions(-)

diff --git a/pandas/_libs/tslibs/tzconversion.pyx b/pandas/_libs/tslibs/tzconversion.pyx
index a096b2807c640..afcf06f04e500 100644
--- a/pandas/_libs/tslibs/tzconversion.pyx
+++ b/pandas/_libs/tslibs/tzconversion.pyx
@@ -347,34 +347,27 @@ cpdef int64_t tz_convert_single(int64_t val, tzinfo tz1, tzinfo tz2):
     cdef:
         int64_t utc_date
         int64_t arr[1]
+        bint to_utc = is_utc(tz2)
+        tzinfo tz
 
     # See GH#17734 We should always be converting either from UTC or to UTC
-    assert is_utc(tz1) or is_utc(tz2)
+    assert is_utc(tz1) or to_utc
 
     if val == NPY_NAT:
         return val
 
-    # Convert to UTC
-    if is_tzlocal(tz1):
-        utc_date = _tz_convert_tzlocal_utc(val, tz1, to_utc=True)
-    elif not is_utc(tz1):
-        arr[0] = val
-        utc_date = _tz_convert_dst(arr, tz1, to_utc=True)[0]
+    if to_utc:
+        tz = tz1
     else:
-        utc_date = val
+        tz = tz2
 
-    if is_utc(tz2):
-        return utc_date
-    elif is_tzlocal(tz2):
-        return _tz_convert_tzlocal_utc(utc_date, tz2, to_utc=False)
+    if is_utc(tz):
+        return val
+    elif is_tzlocal(tz):
+        return _tz_convert_tzlocal_utc(val, tz, to_utc=to_utc)
     else:
-        # Convert UTC to other timezone
-        arr[0] = utc_date
-        # Note: at least with cython 0.28.3, doing a lookup `[0]` in the next
-        # line is sensitive to the declared return type of _tz_convert_dst;
-        # if it is declared as returning ndarray[int64_t], a compile-time error
-        # is raised.
-        return _tz_convert_dst(arr, tz2, to_utc=False)[0]
+        arr[0] = val
+        return _tz_convert_dst(arr, tz, to_utc=to_utc)[0]
 
 
 def tz_convert(int64_t[:] vals, tzinfo tz1, tzinfo tz2):
@@ -393,13 +386,21 @@ def tz_convert(int64_t[:] vals, tzinfo tz1, tzinfo tz2):
     """
     cdef:
         int64_t[:] utc_dates, converted
+        bint to_utc = is_utc(tz2)
+        tzinfo tz
+
+    # See GH#17734 We should always be converting either from UTC or to UTC
+    assert is_utc(tz1) or to_utc
 
     if len(vals) == 0:
         return np.array([], dtype=np.int64)
 
-    # 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)
+    if to_utc:
+        tz = tz1
+    else:
+        tz = tz2
+
+    converted = _tz_convert_one_way(vals, tz, to_utc=to_utc)
     return np.array(converted, dtype=np.int64)
 
 
diff --git a/pandas/tests/tslibs/test_conversion.py b/pandas/tests/tslibs/test_conversion.py
index fd8c9df026674..3a7e06fb14a5f 100644
--- a/pandas/tests/tslibs/test_conversion.py
+++ b/pandas/tests/tslibs/test_conversion.py
@@ -57,9 +57,10 @@ def test_tz_convert_single_matches_tz_convert(tz_aware_fixture, freq):
     ],
 )
 def test_tz_convert_corner(arr):
-    result = tzconversion.tz_convert(
-        arr, timezones.maybe_get_tz("US/Eastern"), timezones.maybe_get_tz("Asia/Tokyo")
-    )
+    result = tzconversion.tz_convert(arr, timezones.maybe_get_tz("US/Eastern"), UTC)
+    tm.assert_numpy_array_equal(result, arr)
+
+    result = tzconversion.tz_convert(arr, UTC, timezones.maybe_get_tz("Asia/Tokyo"))
     tm.assert_numpy_array_equal(result, arr)
 
 

From fc089c5be0f446fdd859b3f2e60f872ed54ff1b3 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Wed, 1 Jul 2020 09:59:47 -0700
Subject: [PATCH 2/2] CLN: remove unused

---
 pandas/_libs/tslibs/tzconversion.pyx | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/pandas/_libs/tslibs/tzconversion.pyx b/pandas/_libs/tslibs/tzconversion.pyx
index afcf06f04e500..d1d6bc40ef288 100644
--- a/pandas/_libs/tslibs/tzconversion.pyx
+++ b/pandas/_libs/tslibs/tzconversion.pyx
@@ -345,7 +345,6 @@ cpdef int64_t tz_convert_single(int64_t val, tzinfo tz1, tzinfo tz2):
     converted: int64
     """
     cdef:
-        int64_t utc_date
         int64_t arr[1]
         bint to_utc = is_utc(tz2)
         tzinfo tz
@@ -385,7 +384,7 @@ def tz_convert(int64_t[:] vals, tzinfo tz1, tzinfo tz2):
     int64 ndarray of converted
     """
     cdef:
-        int64_t[:] utc_dates, converted
+        int64_t[:] converted
         bint to_utc = is_utc(tz2)
         tzinfo tz