Move UTC definition into dateutil.tz.tz

To allow the UTC object to be accessible from the functions in
`dateutil.tz.tz` such as `gettz` and datetime_exists, it is necessary to
define the UTC constant here and import it into `dateutil.tz`. This is a
very minor performance improvement, avoiding a call to the `tzutc()`
constructor.

2 files changed, 6 insertions, 5 deletions

diff --git a/dateutil/tz/__init__.py b/dateutil/tz/__init__.py
index 5a2d9cd..af1352c 100644
--- a/dateutil/tz/__init__.py
+++ b/dateutil/tz/__init__.py
@@ -2,11 +2,6 @@
 from .tz import *
 from .tz import __doc__
 
-#: Convenience constant providing a :class:`tzutc()` instance
-#:
-#: .. versionadded:: 2.7.0
-UTC = tzutc()
-
 __all__ = ["tzutc", "tzoffset", "tzlocal", "tzfile", "tzrange",
            "tzstr", "tzical", "tzwin", "tzwinlocal", "gettz",
            "enfold", "datetime_ambiguous", "datetime_exists",
diff --git a/dateutil/tz/tz.py b/dateutil/tz/tz.py
index d05414e..bef0a9c 100644
--- a/dateutil/tz/tz.py
+++ b/dateutil/tz/tz.py
@@ -123,6 +123,12 @@ class tzutc(datetime.tzinfo):
     __reduce__ = object.__reduce__
 
 
+#: Convenience constant providing a :class:`tzutc()` instance
+#:
+#: .. versionadded:: 2.7.0
+UTC = tzutc()
+
+
 @six.add_metaclass(_TzOffsetFactory)
 class tzoffset(datetime.tzinfo):
     """