Class Instances

Describing Class Instances

• Instances of a class are created by calling a class object as a function
• The following is an instance of a class:

>>> class Foo(object):
...    def __init__(self, bar):
...        self.bar = bar
>>> f = Foo()  # f is new instance

• In other words, calling Foo() creates a new instance
• The instance is initially passed to the __init__() method

• The arguments to __init__() consist of:

  • The newly created instance self
  • Other arguments given to the instance (i.e. bar)

Details about Initializing Instances

• Inside __init__(), attributes are saved in the instance
• This is achieved by assigning attributes to self
• For example, self.bar = bar is saving an attribute bar in the instance f
• These attributes are accessed using the . operator
• Specifically, the dot operator is used for attribute binding

• When accessing an attribute:

  1. The instance is checked first
  2. Then, the instance's class is checked
• This is the underlying mechanism by which a class shares its attributes with all of its instances

References

• Python Essential Reference