CS105: Introduction to Python

The init method (short for "initialization") is a special method that gets invoked when an object is instantiated. Its full name is __init__ (two underscore characters, followed by init, and then two more underscores). An init method for the Time class might look like this:

# inside class Time:

    def __init__(self, hour=0, minute=0, second=0):
        self.hour = hour
        self.minute = minute
        self.second = second

It is common for the parameters of __init__ to have the same names as the attributes. The statement

        self.hour = hour

stores the value of the parameter hour as an attribute of self.

The parameters are optional, so if you call Time with no arguments, you get the default values.

>>> time = Time()
>>> time.print_time()
00:00:00

If you provide one argument, it overrides hour:

>>> time = Time (9)
>>> time.print_time()
09:00:00

If you provide two arguments, they override hour and minute.

>>> time = Time(9, 45)
>>> time.print_time()
09:45:00

And if you provide three arguments, they override all three default values.

As an exercise, write an init method for the Point class that takes x and y as optional parameters and assigns them to the corresponding attributes.