Allow partial minutes for python 3.6 or newer

- Add "Africa/Monrovia" to test_resolve_imaginary test for python 3.6 or newer
- Test that partial minutes is supported in python 3.6 or newer for tz.tzfile and datetime.utcoffset
- Enable partial minutes in both tz.tzoffset and tz.tzfile
- For now, don't warn user when rounding to nearest minute for python pre-3.6

2 files changed, 55 insertions, 25 deletions

diff --git a/dateutil/test/test_tz.py b/dateutil/test/test_tz.py
index 9ae59c7..48b6ae8 100644
--- a/dateutil/test/test_tz.py
+++ b/dateutil/test/test_tz.py
@@ -156,6 +156,8 @@ END:VTIMEZONE
 EST_TUPLE = ('EST', timedelta(hours=-5), timedelta(hours=0))
 EDT_TUPLE = ('EDT', timedelta(hours=-4), timedelta(hours=1))
 
+SUPPORTS_PARTIAL_MINUTES = sys.version_info >= (3, 6)
+
 
 ###
 # Helper functions
@@ -1908,11 +1910,31 @@ class TZTest(unittest.TestCase):
         tzc = tz.tzfile(fileobj)
         self.assertEqual(repr(tzc), 'tzfile(' + repr('foo') + ')')
 
-    def testRoundNonFullMinutes(self):
+    @pytest.mark.skipif(not SUPPORTS_PARTIAL_MINUTES, reason='Partial minute offset supported')
+    def testPartialMinuteSupportTzfile(self):
+        # If user running python 3.6 or newer, exact offset is used
+        tzc = tz.tzfile(BytesIO(base64.b64decode(EUROPE_HELSINKI)))
+        assert datetime(1900, 1, 1, 0, 0, tzinfo=tzc).utcoffset() == timedelta(hours=1, minutes=39, seconds=52)
+
+    @pytest.mark.skipif(not SUPPORTS_PARTIAL_MINUTES, reason='Partial minute offset supported')
+    def testPartialMinuteSupportTimedelta(self):
+        delta = timedelta(hours=12, seconds=30)
+        test_date = datetime(2000, 1, 1, tzinfo=tz.tzoffset(None, delta))
+        assert test_date.utcoffset() == delta
+
+    @pytest.mark.skipif(SUPPORTS_PARTIAL_MINUTES, reason='Partial minute offset not supported')
+    def testRoundNonFullMinutesTzfile(self):
         # This timezone has an offset of 5992 seconds in 1900-01-01.
+        # For python version pre-3.6, this will be rounded
         tzc = tz.tzfile(BytesIO(base64.b64decode(EUROPE_HELSINKI)))
-        self.assertEqual(str(datetime(1900, 1, 1, 0, 0, tzinfo=tzc)),
-                             "1900-01-01 00:00:00+01:40")
+        assert datetime(1900, 1, 1, 0, 0, tzinfo=tzc).utcoffset() == timedelta(hours=1, minutes=40)
+
+    @pytest.mark.skipif(SUPPORTS_PARTIAL_MINUTES, reason='Partial minute offset not supported')
+    def testRoundNonFullMinutesTimedelta(self):
+        delta = timedelta(hours=12, seconds=30)
+        test_date = datetime(2000, 1, 1, tzinfo=tz.tzoffset(None, delta))
+        assert test_date.utcoffset() == timedelta(hours=12, minutes=1)
+
 
     def testLeapCountDecodesProperly(self):
         # This timezone has leapcnt, and failed to decode until
@@ -2617,9 +2639,7 @@ def __get_kiritimati_resolve_imaginary_test():
 
     return (tzi, ) + dates
 
-
-@pytest.mark.tz_resolve_imaginary
-@pytest.mark.parametrize('tzi, dt, dt_exp', [
+resolve_imaginary_tests = [
     (tz.gettz('Europe/London'),
      datetime(2018, 3, 25, 1, 30), datetime(2018, 3, 25, 2, 30)),
     (tz.gettz('America/New_York'),
@@ -2627,24 +2647,19 @@ def __get_kiritimati_resolve_imaginary_test():
     (tz.gettz('Australia/Sydney'),
      datetime(2014, 10, 5, 2, 0), datetime(2014, 10, 5, 3, 0)),
     __get_kiritimati_resolve_imaginary_test(),
-])
+]
+
+if SUPPORTS_PARTIAL_MINUTES:
+    resolve_imaginary_tests.append(
+        (tz.gettz('Africa/Monrovia'),
+         datetime(1972, 1, 7, 0, 30), datetime(1972, 1, 7, 1, 14, 30)))
+
+@pytest.mark.tz_resolve_imaginary
+@pytest.mark.parametrize('tzi, dt, dt_exp', resolve_imaginary_tests)
 def test_resolve_imaginary(tzi, dt, dt_exp):
     dt = dt.replace(tzinfo=tzi)
     dt_exp = dt_exp.replace(tzinfo=tzi)
 
-    dt_r = tz.resolve_imaginary(dt)
-    assert dt_r == dt_exp
-    assert dt_r.tzname() == dt_exp.tzname()
-    assert dt_r.utcoffset() == dt_exp.utcoffset()
-
-
-@pytest.mark.xfail
-@pytest.mark.tz_resolve_imaginary
-def test_resolve_imaginary_monrovia():
-    # See GH #582 - When that is resolved, move this into test_resolve_imaginary
-    tzi = tz.gettz('Africa/Monrovia')
-    dt = datetime(1972, 1, 7, hour=0, minute=30, second=0, tzinfo=tzi)
-    dt_exp = datetime(1972, 1, 7, hour=1, minute=14, second=30, tzinfo=tzi)
 
     dt_r = tz.resolve_imaginary(dt)
     assert dt_r == dt_exp
diff --git a/dateutil/tz/tz.py b/dateutil/tz/tz.py
index f10c1aa..a9ed663 100644
--- a/dateutil/tz/tz.py
+++ b/dateutil/tz/tz.py
@@ -29,6 +29,9 @@ try:
 except ImportError:
     tzwin = tzwinlocal = None
 
+# For warning about rounding tzinfo
+from warnings import warn
+
 ZERO = datetime.timedelta(0)
 EPOCH = datetime.datetime.utcfromtimestamp(0)
 EPOCHORDINAL = EPOCH.toordinal()
@@ -138,7 +141,8 @@ class tzoffset(datetime.tzinfo):
             offset = offset.total_seconds()
         except (TypeError, AttributeError):
             pass
-        self._offset = datetime.timedelta(seconds=offset)
+
+        self._offset = datetime.timedelta(seconds=_get_supported_offset(offset))
 
     def utcoffset(self, dt):
         return self._offset
@@ -601,10 +605,7 @@ class tzfile(_tzinfo):
         out.ttinfo_list = []
         for i in range(typecnt):
             gmtoff, isdst, abbrind = ttinfo[i]
-            # Round to full-minutes if that's not the case. Python's
-            # datetime doesn't accept sub-minute timezones. Check
-            # http://python.org/sf/1447945 for some information.
-            gmtoff = 60 * ((gmtoff + 30) // 60)
+            gmtoff = _get_supported_offset(gmtoff)
             tti = _ttinfo()
             tti.offset = gmtoff
             tti.dstoffset = datetime.timedelta(0)
@@ -1769,6 +1770,20 @@ def _datetime_to_timestamp(dt):
     return (dt.replace(tzinfo=None) - EPOCH).total_seconds()
 
 
+if sys.version_info >= (3, 6):
+    def _get_supported_offset(second_offset):
+        return second_offset
+else:
+    def _get_supported_offset(second_offset):
+        # For python pre-3.6, round to full-minutes if that's not the case.
+        # Python's datetime doesn't accept sub-minute timezones. Check
+        # http://python.org/sf/1447945 or https://bugs.python.org/issue5288
+        # for some information.
+        old_offset = second_offset
+        calculated_offset = 60 * ((second_offset + 30) // 60)
+        return calculated_offset
+
+
 class _ContextWrapper(object):
     """
     Class for wrapping contexts so that they are passed through in a