Make an HTML calendar in a Notebook and highlight some days...

jupyter_calendar.py

# intended for use in a Jupyter Notebook or similar.
import calendar
from calendar import HTMLCalendar
from IPython.display import HTML

class HighlightedCalendar(HTMLCalendar):
    def __init__(self, highlight_dates={}, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self._highlight_dates = {}
        for color,dates in highlight_dates.items():
            for date in dates:
                self._highlight_dates[date] = color
    
    def formatday(self, day, weekday):
        if day in self._month_highlight:
            return '<td class="%s" bgcolor="%s">%d</td>' % (self.cssclasses[weekday], self._month_highlight[day], day)
        else:
            return super().formatday(day, weekday)
    def formatmonth(self, theyear, themonth, withyear):
        self._month_highlight = {d.day:self._highlight_dates[d] for d in self._highlight_dates.keys() if (d.year==theyear) and (d.month==themonth)}
        return super().formatmonth(theyear, themonth, withyear)
    
# Usage
highlight_dates = {
    'lightgreen': [dt.date(2023,1,1),dt.date(2023,2,2),dt.date(2023,3,5)],
    'lightblue': [dt.date(2023,8,1),dt.date(2023,7,2),dt.date(2023,6,5)]
}
HTML(HighlightedCalendar(highlight_dates=highlight_dates).formatyear(2023))