Fix handling of ambiguous times during DST shift

Author: scttnlsn

pvlib/solarposition.py

@@ -1392,6 +1392,14 @@ def hour_angle(times, longitude, equation_of_time):
         times = times.tz_localize('utc')
     tzs = np.array([ts.utcoffset().total_seconds() for ts in times]) / 3600
 
+    is_dst = []
+    for time in times:
+        dst = time.tzinfo.dst(time)
+        if dst is None:
+            is_dst.append(False)
+        else:
+            is_dst.append(dst > dt.timedelta(seconds=0))
+
     # Some timezones have a DST shift at midnight:
     #   11:59pm -> 1:00am - results in a nonexistent midnight
     #   12:59am -> 12:00am - results in an ambiguous midnight
@@ -1401,7 +1409,7 @@ def hour_angle(times, longitude, equation_of_time):
     # Use Pandas functionality for shifting nonexistent times forward
     # or infering ambiguous times (which arose from normalizing)
     normalized_times = naive_normalized_times.tz_localize(
-        times.tz, nonexistent='shift_forward', ambiguous='infer')
+        times.tz, nonexistent='shift_forward', ambiguous=is_dst)
 
     hrs_minus_tzs = (times - normalized_times) / pd.Timedelta('1h') - tzs
 

pvlib/tests/test_solarposition.py

@@ -677,12 +677,13 @@ def test_hour_angle():
 def test_hour_angle_with_tricky_timezones():
     # tests timezones that have a DST shift at midnight
 
-    eot = np.array([-3.935172, -4.117227])
+    eot = np.array([-3.935172, -4.117227, -4.026295])
 
     longitude = 70.6693
     times = pd.DatetimeIndex([
-        '2014-09-07 10:00:00',
-        '2014-09-07 11:00:00',
+        '2014-11-02 00:00:00',
+        '2014-09-07 01:00:00',
+        '2014-09-07 02:00:00',
     ]).tz_localize('America/Santiago')
 
     with pytest.raises(pytz.exceptions.NonExistentTimeError):
@@ -693,9 +694,10 @@ def test_hour_angle_with_tricky_timezones():
 
     longitude = 82.3666
     times = pd.DatetimeIndex([
-        '2014-11-02 10:00:00',
-        '2014-11-02 11:00:00',
-    ]).tz_localize('America/Havana')
+        '2014-11-02 00:00:00',
+        '2014-11-02 01:00:00',
+        '2014-11-02 02:00:00',
+    ]).tz_localize('America/Havana', ambiguous=[True, False, False])
 
     with pytest.raises(pytz.exceptions.AmbiguousTimeError):
         times.normalize()