From 5e2839f3207a02c05b96d761b2441d1ef4d920d4 Mon Sep 17 00:00:00 2001
From: Baptiste Mispelon <bmispelon@gmail.com>
Date: Fri, 15 Nov 2019 17:30:22 +0100
Subject: [PATCH] Simplified DateFormat.W() and z().

---
 django/utils/dateformat.py | 30 ++----------------------------
 1 file changed, 2 insertions(+), 28 deletions(-)

diff --git a/django/utils/dateformat.py b/django/utils/dateformat.py
index af46a81ce6c..82cb444691d 100644
--- a/django/utils/dateformat.py
+++ b/django/utils/dateformat.py
@@ -208,8 +208,6 @@ class TimeFormat(Formatter):
 
 
 class DateFormat(TimeFormat):
-    year_days = [None, 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334]
-
     def b(self):
         "Month, textual, 3 letters, lowercase; e.g. 'jan'"
         return MONTHS_3[self.data.month]
@@ -316,28 +314,7 @@ class DateFormat(TimeFormat):
 
     def W(self):
         "ISO-8601 week number of year, weeks starting on Monday"
-        # Algorithm from http://www.personal.ecu.edu/mccartyr/ISOwdALG.txt
-        jan1_weekday = self.data.replace(month=1, day=1).weekday() + 1
-        weekday = self.data.weekday() + 1
-        day_of_year = self.z()
-        if day_of_year <= (8 - jan1_weekday) and jan1_weekday > 4:
-            if jan1_weekday == 5 or (jan1_weekday == 6 and calendar.isleap(self.data.year - 1)):
-                week_number = 53
-            else:
-                week_number = 52
-        else:
-            if calendar.isleap(self.data.year):
-                i = 366
-            else:
-                i = 365
-            if (i - day_of_year) < (4 - weekday):
-                week_number = 1
-            else:
-                j = day_of_year + (7 - weekday) + (jan1_weekday - 1)
-                week_number = j // 7
-                if jan1_weekday > 4:
-                    week_number -= 1
-        return week_number
+        return self.data.isocalendar()[1]
 
     def y(self):
         "Year, 2 digits; e.g. '99'"
@@ -349,10 +326,7 @@ class DateFormat(TimeFormat):
 
     def z(self):
         """Day of the year, i.e. 1 to 366."""
-        doy = self.year_days[self.data.month] + self.data.day
-        if self.L() and self.data.month > 2:
-            doy += 1
-        return doy
+        return self.data.timetuple().tm_yday
 
 
 def format(value, format_string):