Add function for determining whether a date falls within British Summer Time.

Author: domdfcoding

domdf_python_tools/dates.py

@@ -53,6 +53,7 @@
 # stdlib
 import datetime
 import sys
+import time
 import typing
 from collections import OrderedDict
 from types import ModuleType
@@ -69,6 +70,7 @@
 		"calc_easter",
 		"month_short_names",
 		"month_full_names",
+		"is_bst",
 		]
 
 
@@ -318,6 +320,43 @@ def get_timezone(tz: str, date: Optional[datetime.datetime] = None) -> Optional[
 	return pytz.timezone(tz).localize(d).tzinfo
 
 
+def is_bst(the_date: Union[time.struct_time, datetime.date]) -> bool:
+	"""
+	Calculates whether the given day falls within British Summer Time.
+
+	This function should also be applicable to other timezones which change to summer time on the same date (e.g. Central European Summer Time).
+
+	.. note::
+
+		This function does not consider the time of day,
+		and therefore does not handle the fact that the time changes at 1 AM GMT.
+		It also does not account for historic deviations from the current norm.
+
+	.. versionadded:: 3.5.0
+
+	:param the_date: A :class:`time.struct_time`, :class:`datetime.date`
+		or :class:`datetime.datetime` representing the target date.
+
+	:returns: :py:obj:`True` if the date falls within British Summer Time, :py:obj:`False` otherwise.
+	"""
+
+	if isinstance(the_date, datetime.date):
+		the_date = the_date.timetuple()
+
+	day, month, dow = the_date.tm_mday, the_date.tm_mon, (the_date.tm_wday + 1) % 7
+
+	if 3 > month > 10:
+		return False
+	elif 3 < month < 10:
+		return True
+	elif month == 3:
+		return day - dow >= 25
+	elif month == 10:
+		return day - dow < 25
+	else:
+		return False
+
+
 _pytz_functions = ["get_utc_offset", "get_timezone"]
 
 try:

tests/test_dates.py

@@ -325,3 +325,64 @@ def test_check_date():
 		)
 def test_calc_easter(date):
 	assert dates.calc_easter(date.year) == date
+
+
+@pytest.mark.parametrize(
+		"the_date, result",
+		[
+				(date(month=3, day=2, year=2019), False),
+				(date(month=4, day=7, year=2020), True),
+				(date(month=8, day=17, year=2015), True),
+				(date(month=12, day=25, year=2030), False),
+				(date(month=3, day=29, year=2019), False),
+				(date(month=3, day=30, year=2019), False),
+				(date(month=3, day=31, year=2019), True),
+				(date(month=4, day=1, year=2019), True),
+				(date(month=10, day=25, year=2019), True),
+				(date(month=10, day=26, year=2019), True),
+				(date(month=10, day=27, year=2019), False),
+				(date(month=10, day=28, year=2019), False),
+				(date(month=3, day=27, year=2020), False),
+				(date(month=3, day=28, year=2020), False),
+				(date(month=3, day=29, year=2020), True),
+				(date(month=3, day=30, year=2020), True),
+				(date(month=10, day=23, year=2020), True),
+				(date(month=10, day=24, year=2020), True),
+				(date(month=10, day=25, year=2020), False),
+				(date(month=10, day=26, year=2020), False),
+				(date(month=3, day=26, year=2021), False),
+				(date(month=3, day=27, year=2021), False),
+				(date(month=3, day=28, year=2021), True),
+				(date(month=3, day=29, year=2021), True),
+				(date(month=10, day=29, year=2021), True),
+				(date(month=10, day=30, year=2021), True),
+				(date(month=10, day=31, year=2021), False),
+				(date(month=11, day=1, year=2021), False),
+				(date(month=3, day=25, year=2022), False),
+				(date(month=3, day=26, year=2022), False),
+				(date(month=3, day=27, year=2022), True),
+				(date(month=3, day=28, year=2022), True),
+				(date(month=10, day=28, year=2022), True),
+				(date(month=10, day=29, year=2022), True),
+				(date(month=10, day=30, year=2022), False),
+				(date(month=10, day=31, year=2022), False),
+				(date(month=3, day=24, year=2023), False),
+				(date(month=3, day=25, year=2023), False),
+				(date(month=3, day=26, year=2023), True),
+				(date(month=3, day=27, year=2023), True),
+				(date(month=10, day=27, year=2023), True),
+				(date(month=10, day=28, year=2023), True),
+				(date(month=10, day=29, year=2023), False),
+				(date(month=10, day=30, year=2023), False),
+				(date(month=3, day=29, year=2024), False),
+				(date(month=3, day=30, year=2024), False),
+				(date(month=3, day=31, year=2024), True),
+				(date(month=4, day=1, year=2024), True),
+				(date(month=10, day=25, year=2024), True),
+				(date(month=10, day=26, year=2024), True),
+				(date(month=10, day=27, year=2024), False),
+				(date(month=10, day=28, year=2024), False),
+				]
+		)
+def test_is_bst(the_date, result: bool):
+	assert dates.is_bst(the_date) is result