An attribute is a capacious term that can refer to two major kinds of class traits:
- variables, containing information about the class itself or a class instance; classes and class instances can own many variables;
- methods, formulated as Python functions; they represent a behavior that could be applied to the object.
Each Python object has its own individual set of attributes. We can extend that set by adding new attributes to existing objects, change (reassign) them or control access to those attributes.
It is said that methods are the 'callable attributes' of Python objects. By 'callable' we should understand anything that can be called; such objects allow you to use round parentheses () and eventually pass some parameters, just like functions.
This is a very important fact to remember: methods are called on behalf of an object and are usually executed on object data.
Class attributes are most often addressed with 'dot' notation, i.e., <class>dot<attribute>. The other way to access attributes (variables) it to use the getattr() and setattr() functions.
In our 'duckish' example, there are the following attributes:
- variables:
self.height,self.weight,self.sex— containing different values for each object; - methods:
__init__,walk,quack— common to all objects so far.
- To call a method, issue:
drake.quack(); - To access an attribute, issue:
print(duckling.height).
If you run the code, you'll get the following example:
Quack
10
output
Code
class Duck:def __init__(self, height, weight, sex):
self.height = height
self.weight = weight
self.sex = sex
def walk(self):
pass
def quack(self):
return print('Quack')
duckling = Duck(height=10, weight=3.4, sex="male")
drake = Duck(height=25, weight=3.7, sex="male")
hen = Duck(height=20, weight=3.4, sex="female")
drake.quack()
print(duckling.height)