BUG: GH12290 where tz_convert used values of uninitialized arrays

closes #12290

Author: Ka Wo Chen <kawoc@tepper.cmu.edu>

Closes #12306 from kawochen/BUG-FIX-12290 and squashes the following commits:

38bed4d [Ka Wo Chen] BUG: GH12290 where tz_convert used values of uninitialized arrays

Author: kawochen

doc/source/whatsnew/v0.18.0.txt

@@ -906,6 +906,7 @@ Bug Fixes
 
 
 - Bug in ``NaT`` subtraction from ``Timestamp`` or ``DatetimeIndex`` with timezones (:issue:`11718`)
+- Bug in subtraction of ``Series`` of a single tz-aware ``Timestamp`` (:issue:`12290`)
 
 - Bug in ``Timedelta.round`` with negative values (:issue:`11690`)
 - Bug in ``.loc`` against ``CategoricalIndex`` may result in normal ``Index`` (:issue:`11586`)

pandas/tests/series/test_operators.py

@@ -660,6 +660,17 @@ def run_ops(ops, get_ser, test_ser):
         self.assertRaises(TypeError, lambda: td1 - dt1)
         self.assertRaises(TypeError, lambda: td2 - dt2)
 
+    def test_sub_single_tz(self):
+        # GH12290
+        s1 = Series([pd.Timestamp('2016-02-10', tz='America/Sao_Paulo')])
+        s2 = Series([pd.Timestamp('2016-02-08', tz='America/Sao_Paulo')])
+        result = s1 - s2
+        expected = Series([Timedelta('2days')])
+        assert_series_equal(result, expected)
+        result = s2 - s1
+        expected = Series([Timedelta('-2days')])
+        assert_series_equal(result, expected)
+
     def test_ops_nat(self):
         # GH 11349
         timedelta_series = Series([NaT, Timedelta('1s')])

pandas/tslib.pyx

@@ -3530,7 +3530,7 @@ def tz_convert(ndarray[int64_t] vals, object tz1, object tz2):
     if _get_zone(tz2) == 'UTC':
         return utc_dates
 
-    result = np.empty(n, dtype=np.int64)
+    result = np.zeros(n, dtype=np.int64)
     if _is_tzlocal(tz2):
         for i in range(n):
             v = utc_dates[i]