DOC/ENH: Holiday days_of_week value error (#61658)

* changed days_of_week to raise ValueError and updated docstring

* moved whatsnew entry to be next to relevant holiday entry

* updated rst to link relevant issue

Author: sharkipelago

doc/source/whatsnew/v3.0.0.rst

@@ -65,6 +65,7 @@ Other enhancements
 - :class:`ArrowDtype` now supports ``pyarrow.JsonType`` (:issue:`60958`)
 - :class:`DataFrameGroupBy` and :class:`SeriesGroupBy` methods ``sum``, ``mean``, ``median``, ``prod``, ``min``, ``max``, ``std``, ``var`` and ``sem`` now accept ``skipna`` parameter (:issue:`15675`)
 - :class:`Easter` has gained a new constructor argument ``method`` which specifies the method used to calculate Easter — for example, Orthodox Easter (:issue:`61665`)
+- :class:`Holiday` constructor argument ``days_of_week`` will raise a ``ValueError`` when type is something other than ``None`` or ``tuple`` (:issue:`61658`)
 - :class:`Holiday` has gained the constructor argument and field ``exclude_dates`` to exclude specific datetimes from a custom holiday calendar (:issue:`54382`)
 - :class:`Rolling` and :class:`Expanding` now support ``nunique`` (:issue:`26958`)
 - :class:`Rolling` and :class:`Expanding` now support aggregations ``first`` and ``last`` (:issue:`33155`)

pandas/tests/tseries/holiday/test_holiday.py

@@ -454,3 +454,10 @@ def test_exclude_date_value_error():
             Timestamp("2026-06-10"),
         ]
         Holiday("National Ice Tea Day", month=6, day=10, exclude_dates=exclude)
+
+
+def test_days_of_week_value_error():
+    msg = "days_of_week must be None or tuple."
+
+    with pytest.raises(ValueError, match=msg):
+        Holiday("World Blood Donor Day", month=6, day=14, days_of_week=[0, 1])

pandas/tseries/holiday.py

@@ -192,8 +192,9 @@ class from pandas.tseries.offsets, default None
         end_date : datetime-like, default None
             Last date the holiday is observed
         days_of_week : tuple of int or dateutil.relativedelta weekday strs, default None
-            Provide a tuple of days e.g  (0,1,2,3,) for Monday Through Thursday
+            Provide a tuple of days e.g  (0,1,2,3,) for Monday through Thursday
             Monday=0,..,Sunday=6
+            Only instances of the holiday included in days_of_week will be computed
         exclude_dates : DatetimeIndex or default None
             Specific dates to exclude e.g. skipping a specific year's holiday
 
@@ -258,7 +259,8 @@ class from pandas.tseries.offsets, default None
         )
         self.end_date = Timestamp(end_date) if end_date is not None else end_date
         self.observance = observance
-        assert days_of_week is None or type(days_of_week) == tuple
+        if not (days_of_week is None or isinstance(days_of_week, tuple)):
+            raise ValueError("days_of_week must be None or tuple.")
         self.days_of_week = days_of_week
         if not (exclude_dates is None or isinstance(exclude_dates, DatetimeIndex)):
             raise ValueError("exclude_dates must be None or of type DatetimeIndex.")