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The init method

8 September, 2015 - 10:43

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.

Exercise 17.2. Write an init method for thePointclass that takesxandyas optional parameters and assigns them to the corresponding attributes.