[Zope3-checkins] CVS: Zope3/src/datetime - _datetime.py:1.4

[Tim Peters]

Update of /cvs-repository/Zope3/src/datetime
In directory cvs.zope.org:/tmp/cvs-serv11249/src/datetime

Modified Files:
	_datetime.py 
Log Message:
timetz comparison, and datetimetz subtraction:  reimplemented these to
work as documented.  They weren't calling utcoffset() if both operands
had the same tzinfo object.  That's fine if it so happens that the
shared tzinfo object returns a fixed offset (independent of operand),
but can give wrong results if that's not so, and the latter obtains in
a tzinfo subclass instance trying to model both standard and daylight
times.

This repairs some of the surprises in the sandbox US.py demo, but
not all of them.  In a way, it makes one part even more surprising:
because addition of datetimetz and timedelta doesn't do anything with
tzinfo except attach it to the result, it's possible to add, e.g.,
one second to a datetimetz, and then see the result of that minus the
original datetimetz span an hour.  This can happen at DST boundaries
(see US.py's doctest for concrete examples).


=== Zope3/src/datetime/_datetime.py 1.3 => 1.4 ===
--- Zope3/src/datetime/_datetime.py:1.3	Wed Dec 25 14:28:50 2002
+++ Zope3/src/datetime/_datetime.py	Wed Dec 25 23:49:46 2002
@@ -1056,12 +1056,6 @@
                             type(other).__name__)
         superself = super(timetz, self)
         supercmp = superself.__cmp__
-        mytz = self.__tzinfo
-        ottz = None
-        if isinstance(other, timetz):
-            ottz = other.__tzinfo
-        if mytz is ottz:
-            return supercmp(other)
         myoff = self._utcoffset()
         otoff = other._utcoffset()
         if myoff == otoff:
@@ -1672,12 +1666,10 @@
     def __sub__(self, other):
         supersub = super(datetimetz, self).__sub__
         if not isinstance(other, datetime):
-            return supersub(other) # XXX should set tzinfo on result
-        mytz = self.__tzinfo
-        ottz = None
-        if isinstance(other, datetimetz):
-            ottz = other.__tzinfo
-        if mytz is ottz:
+            # This manages to attach self.tzinfo to the result via a
+            # devious route:  self - timedelta is changed to
+            # self + (-timedelta) by datetime.__sub__, and the latter is
+            # handled by datetimetz.__add__.
             return supersub(other)
         myoff = self._utcoffset()
         otoff = other._utcoffset()