bugfix: fix an error in get_start_and_end_date_from_calendar_week (#37)

With the current implementation, get_start_and_end_date_from_calendar_week was not able to determine dates, when calendar_week == 1 actually starts before the current year

CHANGES.md

@@ -1,5 +1,8 @@
 # Changelog
 
+**11.5.2** (2024-10-15)
+  * Improved date determination of `get_start_and_end_date_from_calendar_week`
+
 **11.5.1** (2024-10-08)
 * Added Python 3.13 support
 * Added Djade linter to pre-commit

ambient_toolbox/__init__.py

@@ -1,3 +1,3 @@
 """Python toolbox of Ambient Digital containing an abundance of useful tools and gadgets."""
 
-__version__ = "11.5.1"
+__version__ = "11.5.2"

ambient_toolbox/utils/date.py

@@ -94,8 +94,20 @@ def get_start_and_end_date_from_calendar_week(year: int, calendar_week: int) ->
     """
     Returns the first and last day of a given calendar week
     """
-    monday = datetime.datetime.strptime(f"{year}-{calendar_week}-1", "%Y-%W-%w").astimezone().date()
-    return monday, monday + datetime.timedelta(days=6.9)
+    start_of_week = datetime.datetime.strptime(f"{year}-{calendar_week}-1", "%Y-%W-%w").astimezone().date()
+
+    if calendar_week == 1:
+        # Calculating first_day_of_week for calendar_week == 1 is always tricky, as the first calendar week
+        # can actually start in the n-1 year. The above .strptime() can not handle this however, and would always
+        # return the first of January.
+        # For this case, we consider the fourth of january, as it will _always_ be in the first calendar week
+        # (see: https://en.wikipedia.org/wiki/ISO_week_date#First_week)
+
+        fourth_of_january = datetime.date(year=year, month=1, day=4)
+
+        start_of_week = fourth_of_january - relativedelta(days=fourth_of_january.weekday())
+
+    return start_of_week, start_of_week + relativedelta(days=6)
 
 
 def get_next_calendar_week(compare_date: datetime.date) -> int:

tests/test_utils_date.py

@@ -38,6 +38,10 @@ def test_get_start_and_end_date_from_calendar_week(self):
         self.assertEqual(monday, datetime.date(year=2018, month=1, day=1))
         self.assertEqual(sunday, datetime.date(year=2018, month=1, day=7))
 
+        monday, sunday = get_start_and_end_date_from_calendar_week(2020, 1)
+        self.assertEqual(monday, datetime.date(year=2019, month=12, day=30))
+        self.assertEqual(sunday, datetime.date(year=2020, month=1, day=5))
+
         monday, sunday = get_start_and_end_date_from_calendar_week(2017, 30)
         self.assertEqual(monday, datetime.date(year=2017, month=7, day=24))
         self.assertEqual(sunday, datetime.date(year=2017, month=7, day=30))