Methods¶

Methods are essentially normal functions which must be called using that object and always have at least 1 argument. They are defined with the def keyword but they are “attached” to an object.

The first argument to the method is always treated as a reference to the object that called the method and the standard convention is to name the variable self.

Python puts the self argument in automatically. For example, we can add a sleep() method to our Person class:

class Person(object):

    name = "Bob"

    def sleep(self):
        print(self.name + ' is sleeping')

The method can only be used through an object so one must have been constructed first, e.g.

person1 = Person()
# Note: We call it with no arguments, Python inserts self automatically.
# We use parentheses because sleep is a function
person1.sleep()

Other than the self argument, methods behave in the same manner as standard functions and you can take any additional arguments required:

class Person(object):

    name = "Bob"

    def sleep(self, nhours):
        print(self.name + ' is sleeping for ' + str(nhours) + ' hours')

##################################################################
person1 = Person()
# Called with 1 argument, Python inserts the self automatically.
person1.sleep(7)

class Person(object):
    def __init__(self, name):
        # Add a 'name' field to the object and assign a value to it.
        self.name = name

    def sleep(self):
        print(self.name +' is sleeping')

###################################################

# Usage:
person1 = Person("Bob")
person2 = Person("Alice")

person1.sleep() # => prints "Bob is sleeping"
person2.sleep() # => prints "Alice is sleeping"