Static Methods

Before

class Calendar:
    
    def __init__(self, date):
        self.year = date.year
        self.month = date.month
        self.day = date.day
        self.weekday = date.weekday()
    
    
    def is_leap_year(self):
        return self.year % 400 == 0 or 
               (self.year % 4 == 0 and self.year % 100 != 0)
    
    
    def is_weekend(self):
        return self.weekday > 4

We want to decouple the is_weekend and is_leap_year from the calendar class instance because they relate to any date not just that class instance.

After

class Calendar:
    
    def __init__(self, date):
        self.year = date.year
        self.month = date.month
        self.day = date.day
        self.weekday = date.weekday()
    
    
    @staticmethod
    def is_leap_year(date):
        return date.year % 400 == 0 or 
        (date.year % 4 == 0 and date.year % 100 != 0)
    
    
    @staticmethod
    def is_weekend(date):
        return date.weekday() > 4

Ok, the changes are:

1. Add the decorator @staticmethod;
2. Rename the expected parameter to be a date object;
3. Adjust the is_weekend function to get weekday as function and not variable.

Usage: