Improve example on tzinfo instances

Move from GMTX to TZX when naming the classes, as GMT1 might be rather
confusing as seen in the reported issue.
In addition, move to UTC over GMT and improve the tzname implementation.

Author: mariocj89

Doc/library/datetime.rst

@@ -1317,7 +1317,7 @@ Examples of working with datetime objects:
 Using datetime with tzinfo:
 
     >>> from datetime import timedelta, datetime, tzinfo
-    >>> class GMT1(tzinfo):
+    >>> class TZ1(tzinfo):
     ...     def utcoffset(self, dt):
     ...         return timedelta(hours=1) + self.dst(dt)
     ...     def dst(self, dt):
@@ -1331,9 +1331,9 @@ Using datetime with tzinfo:
     ...         else:
     ...             return timedelta(0)
     ...     def tzname(self,dt):
-    ...          return "GMT +1"
+    ...         return "UTC +2" if self.dst(dt) else "UTC +1"
     ...
-    >>> class GMT2(tzinfo):
+    >>> class TZ2(tzinfo):
     ...     def utcoffset(self, dt):
     ...         return timedelta(hours=2) + self.dst(dt)
     ...     def dst(self, dt):
@@ -1346,26 +1346,26 @@ Using datetime with tzinfo:
     ...         else:
     ...             return timedelta(0)
     ...     def tzname(self,dt):
-    ...         return "GMT +2"
+    ...         return "UTC +3" if self.dst(dt) else "UTC +2"
     ...
-    >>> gmt1 = GMT1()
+    >>> tz1 = TZ1()
     >>> # Daylight Saving Time
-    >>> dt1 = datetime(2006, 11, 21, 16, 30, tzinfo=gmt1)
+    >>> dt1 = datetime(2006, 11, 21, 16, 30, tzinfo=tz1)
     >>> dt1.dst()
     datetime.timedelta(0)
     >>> dt1.utcoffset()
     datetime.timedelta(seconds=3600)
-    >>> dt2 = datetime(2006, 6, 14, 13, 0, tzinfo=gmt1)
+    >>> dt2 = datetime(2006, 6, 14, 13, 0, tzinfo=tz1)
     >>> dt2.dst()
     datetime.timedelta(seconds=3600)
     >>> dt2.utcoffset()
     datetime.timedelta(seconds=7200)
     >>> # Convert datetime to another time zone
-    >>> dt3 = dt2.astimezone(GMT2())
+    >>> dt3 = dt2.astimezone(TZ2())
     >>> dt3     # doctest: +ELLIPSIS
-    datetime.datetime(2006, 6, 14, 14, 0, tzinfo=<GMT2 object at 0x...>)
+    datetime.datetime(2006, 6, 14, 14, 0, tzinfo=<TZ2 object at 0x...>)
     >>> dt2     # doctest: +ELLIPSIS
-    datetime.datetime(2006, 6, 14, 13, 0, tzinfo=<GMT1 object at 0x...>)
+    datetime.datetime(2006, 6, 14, 13, 0, tzinfo=<TZ1 object at 0x...>)
     >>> dt2.utctimetuple() == dt3.utctimetuple()
     True
 
@@ -1591,26 +1591,25 @@ Instance methods:
 Example:
 
     >>> from datetime import time, tzinfo, timedelta
-    >>> class GMT1(tzinfo):
+    >>> class TZ1(tzinfo):
     ...     def utcoffset(self, dt):
     ...         return timedelta(hours=1)
     ...     def dst(self, dt):
     ...         return timedelta(0)
     ...     def tzname(self,dt):
-    ...         return "Europe/Prague"
+    ...         return "UTC+1"
     ...
-    >>> t = time(12, 10, 30, tzinfo=GMT1())
+    >>> t = time(12, 10, 30, tzinfo=TZ1())
     >>> t                               # doctest: +ELLIPSIS
-    datetime.time(12, 10, 30, tzinfo=<GMT1 object at 0x...>)
-    >>> gmt = GMT1()
+    datetime.time(12, 10, 30, tzinfo=<TZ1 object at 0x...>)
     >>> t.isoformat()
     '12:10:30+01:00'
     >>> t.dst()
     datetime.timedelta(0)
     >>> t.tzname()
-    'Europe/Prague'
+    'UTC+1'
     >>> t.strftime("%H:%M:%S %Z")
-    '12:10:30 Europe/Prague'
+    '12:10:30 UTC+1'
     >>> 'The {} is {:%H:%M}.'.format("time", t)
     'The time is 12:10.'