From e11b510a5b35378572aca75dae7e9174756da5da Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <python@rcn.com>
Date: Wed, 25 Dec 2002 16:37:19 +0000
Subject: [PATCH] SF 658405:  calendar.py to rely on the datetime module
 instead of the time module.

The code is shorter, more readable, faster, and dramatically increases the
range of acceptable dates.

Also, used the floor division operator in leapdays().
---
 Doc/lib/libcalendar.tex | 10 ++++++----
 Lib/calendar.py         | 26 ++++++++------------------
 Misc/NEWS               |  4 ++++
 3 files changed, 18 insertions(+), 22 deletions(-)

diff --git a/Doc/lib/libcalendar.tex b/Doc/lib/libcalendar.tex
index 222e2dbbb9e..bf0c85bc2cb 100644
--- a/Doc/lib/libcalendar.tex
+++ b/Doc/lib/libcalendar.tex
@@ -15,10 +15,12 @@ convention). Use \function{setfirstweekday()} to set the first day of the
 week to Sunday (6) or to any other weekday.  Parameters that specify
 dates are given as integers.
 
-Most of these functions rely on the platform provided \function{mktime()}.
-Therefore, valid argument values may vary from system to system.
-On Unix, valid years are typically between \code{1970} and \code{2037},
-but may be work between \code{1902} and \code{2037}.
+Most of these functions rely on the \module{datetime} module which
+uses an idealized calendar, the current Gregorian calendar indefinitely
+extended in both directions.  This matches the definition of the
+"proleptic Gregorian" calendar in Dershowitz and Reingold's book
+"Calendrical Calculations", where it's the base calendar for all
+computations.
 
 \begin{funcdesc}{setfirstweekday}{weekday}
 Sets the weekday (\code{0} is Monday, \code{6} is Sunday) to start
diff --git a/Lib/calendar.py b/Lib/calendar.py
index 3f9b7ba9740..365ca263444 100644
--- a/Lib/calendar.py
+++ b/Lib/calendar.py
@@ -5,10 +5,7 @@
 Sunday as the last (the European convention). Use setfirstweekday() to
 set the first day of the week (0=Monday, 6=Sunday)."""
 
-# Revision 2: uses functions from built-in time module
-
-# Import functions and variables from time module
-from time import localtime, mktime, strftime
+import datetime
 
 __all__ = ["error","setfirstweekday","firstweekday","isleap",
            "leapdays","weekday","monthrange","monthcalendar",
@@ -35,7 +32,7 @@ def __init__(self, format):
         self.format = format
 
     def __getitem__(self, i):
-        data = [strftime(self.format, (2001, j, 1, 12, 0, 0, 1, 1, 0))
+        data = [datetime.date(2001, j, 1).strftime(self.format)
                      for j in range(1, 13)]
         data.insert(0, "")
         return data[i]
@@ -49,7 +46,7 @@ def __init__(self, format):
 
     def __getitem__(self, i):
         # January 1, 2001, was a Monday.
-        data = [strftime(self.format, (2001, 1, j+1, 12, 0, 0, j, j+1, 0))
+        data = [datetime.date(2001, 1, j+1).strftime(self.format)
                      for j in range(7)]
         return data[i]
 
@@ -89,14 +86,12 @@ def leapdays(y1, y2):
        Assume y1 <= y2."""
     y1 -= 1
     y2 -= 1
-    return (y2/4 - y1/4) - (y2/100 - y1/100) + (y2/400 - y1/400)
+    return (y2//4 - y1//4) - (y2//100 - y1//100) + (y2//400 - y1//400)
 
 def weekday(year, month, day):
     """Return weekday (0-6 ~ Mon-Sun) for year (1970-...), month (1-12),
        day (1-31)."""
-    secs = mktime((year, month, day, 0, 0, 0, 0, 0, 0))
-    tuple = localtime(secs)
-    return tuple[6]
+    return datetime.date(year, month, day).weekday()
 
 def monthrange(year, month):
     """Return weekday (0-6 ~ Mon-Sun) and number of days (28-31) for
@@ -213,17 +208,12 @@ def calendar(year, w=0, l=0, c=_spacing):
     return s[:-l] + '\n'
 
 EPOCH = 1970
+_EPOCH_ORD = datetime.date(EPOCH, 1, 1).toordinal()
+
 def timegm(tuple):
     """Unrelated but handy function to calculate Unix timestamp from GMT."""
     year, month, day, hour, minute, second = tuple[:6]
-    assert year >= EPOCH
-    assert 1 <= month <= 12
-    days = 365*(year-EPOCH) + leapdays(EPOCH, year)
-    for i in range(1, month):
-        days = days + mdays[i]
-    if month > 2 and isleap(year):
-        days = days + 1
-    days = days + day - 1
+    days = datetime.date(year, month, day).toordinal() - _EPOCH_ORD
     hours = days*24 + hour
     minutes = hours*60 + minute
     seconds = minutes*60 + second
diff --git a/Misc/NEWS b/Misc/NEWS
index 5cc62bf198a..a9e3803eba3 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -443,6 +443,10 @@ Extension modules
 Library
 -------
 
+- calendar.py now depends on the new datetime module rather than
+  the time module.  As a result, the range of allowable dates
+  has been increased.
+
 - pdb has a new 'j(ump)' command to select the next line to be
   executed.