1 files changed, 62 insertions, 1 deletions
diff --git a/Doc/lib/tzinfo-examples.py b/Doc/lib/tzinfo-examples.py
index 92f298c..70a4966 100644
--- a/Doc/lib/tzinfo-examples.py
+++ b/Doc/lib/tzinfo-examples.py
@@ -1,6 +1,7 @@
-from datetime import tzinfo, timedelta
+from datetime import tzinfo, timedelta, datetime
 
 ZERO = timedelta(0)
+HOUR = timedelta(hours=1)
 
 # A UTC class.
 
@@ -76,3 +77,63 @@ class LocalTimezone(tzinfo):
         return tt.tm_isdst > 0
 
 Local = LocalTimezone()
+
+
+# A complete implementation of current DST rules for major US time zones.
+
+def first_sunday_on_or_after(dt):
+    days_to_go = 6 - dt.weekday()
+    if days_to_go:
+        dt += timedelta(days_to_go)
+    return dt
+
+# In the US, DST starts at 2am (standard time) on the first Sunday in April.
+DSTSTART = datetime(1, 4, 1, 2)
+# and ends at 2am (DST time; 1am standard time) on the last Sunday of Oct.
+# which is the first Sunday on or after Oct 25.
+DSTEND = datetime(1, 10, 25, 2)
+
+class USTimeZone(tzinfo):
+
+    def __init__(self, hours, reprname, stdname, dstname):
+        self.stdoffset = timedelta(hours=hours)
+        self.reprname = reprname
+        self.stdname = stdname
+        self.dstname = dstname
+
+    def __repr__(self):
+        return self.reprname
+
+    def tzname(self, dt):
+        if self.dst(dt):
+            return self.dstname
+        else:
+            return self.stdname
+
+    def utcoffset(self, dt):
+        return self.stdoffset + self.dst(dt)
+
+    def dst(self, dt):
+        if dt is None or dt.tzinfo is None:
+            # An exception may be sensible here, in one or both cases.
+            # It depends on how you want to treat them.  The astimezone()
+            # implementation always passes a datetimetz with
+            # dt.tzinfo == self.
+            return ZERO
+        assert dt.tzinfo is self
+
+        # Find first Sunday in April & the last in October.
+        start = first_sunday_on_or_after(DSTSTART.replace(year=dt.year))
+        end = first_sunday_on_or_after(DSTEND.replace(year=dt.year))
+
+        # Can't compare naive to aware objects, so strip the timezone from
+        # dt first.
+        if start <= dt.replace(tzinfo=None) < end:
+            return HOUR
+        else:
+            return ZERO
+
+Eastern  = USTimeZone(-5, "Eastern",  "EST", "EDT")
+Central  = USTimeZone(-6, "Central",  "CST", "CDT")
+Mountain = USTimeZone(-7, "Mountain", "MST", "MDT")
+Pacific  = USTimeZone(-8, "Pacific",  "PST", "PDT")