Manage and Use Class Properties

Q

How to manage and use class properties?

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A

Class properties, also called class attributes, are name value pairs associated with class "type" object, and shared among all instances (objects) created from this class.

You can manage and use class properties in various places:

1. In the class definition statement block - You can add new class property and assign its initial value in the class definition statement block. In this case, you can use the property name as a variable name directly.

>>> class user():
...     nextID = 1
...     def method():
...         ...

2. In any method definition statement block of the class - You can add new class property, assign its initial value, access its value and change its value in any method definition statement block of the class. In this case, you need to include the class name in the dot (.) expression to cross the scope boundary: class_name.property_name. For example:

>>> class user():
...     nextID = 1
...     def __init__(self,name="Joe",age=25):
...         user.alert = "'user' object created!"
...         self.id = user.nextID
...         user.nextID = user.nextID + 1
...         ...

3. In any Python code after the class is defined - You can add new class property, assign its initial value, access its value and change its value in any Python code after the class is defined (the class definition statement block has been interpreted). In this case, you need to include the class name in the dot (.) expression to cross the scope boundary: class_name.property_name. For example:

>>> class user():
...     ...
...
>>> user.instanceCount = 0
>>> a = user()
>>> user.instanceCount = user.instanceCount + 1
>>> b = user()
>>> user.instanceCount = user.instanceCount + 1
>>> user.instanceCount
2

 

Defining and Using Class for New Data Types

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2017-09-09, 117👍, 0💬