Object Orientation in Python - More About Creating Classes (Page 4 of 4 )
I mentioned subclasses and inheritance in the previous section. We will now take a look at how to create a class that derives its methods and variables from another class:
class ParentClass:
testVariableOne = 'This is a test. I promise.'
testVariableTwo = 'No, really, it is just a test.'
def __init__ ( self, testArgument ):
self.testVariableThree = testArgument
def testMethod ( self ):
pass
class ChildClass ( ParentClass ):
pass
parentObject = ParentClass ( 'Hello, how are you?' )
print parentObject.testVariableOne # "This is a test. I promise."
print parentObject.testVariableTwo # "No, really, it is just a test."
print parentObject.testVariableThree # "Hello, how are you?"
childObject = ChildClass ( 'I am fine, thank you.' )
print childObject.testVariableOne # "This is a test. I promise."
print childObject.testVariableTwo # "No, really, it is just a test."
print childObject.testVariableThree # "I am fine, thank you."
Subclasses are perfectly capable of defining their own variables and methods, too. They can also overwrite variables and methods passed down from the original class:
class ParentClass:
testVariableA = 'This is a test variable. Pay no attention to it.'
testVariableB = 'This is also a test variable. Or is it? We may never know.'
def __init__ ( self, testArgument ):
self.testVariableC = testArgument
def testMethod ( self ):
return False
class ChildClass ( ParentClass ):
testVariableB = 'I am a very rebellious variable. Yes I am.'
def testMethod ( self ):
return True
parentObject = ParentClass ( 'I am an insignificant test argument.' )
print parentObject.testVariableA # "This is a test variable. Pay no attention to it."
print parentObject.testVariableB # "This is a test variable. Or is it? We may never know."
print parentObject.testVariableC # "I am an insignificant test argument"
print parentObject.testMethod() # False
childObject = ChildClass ( 'This is a subclass of ParentClass.' )
print childObject.testVariableA # "This is a test variable. Pay no attention to it."
print childObject.testVariableB # "I am a very rebellious variable. Yes I am."
print childObject.testVariableC # "This is a subclass of Parent Class."
print childObject.testMethod() # True
If you only want to add to a parent's method, this is also possible by calling the class's method and supplying the needed arguments:
class ParentClass:
def testMethod ( self, testArgument ):
return str ( len ( testArgument ) )
class ChildClass:
def testMethod ( self, testArgument ):
return ParentClass.testMethod ( self, testArgument ) + ' ( Extra Stuff )'
parentObject = ParentClass()
print parentObject.testMethod ( 'This is a long string.' ) # "22"
childObject =ChildClass()
print childObject.testMethod ( 'This is a long string.' ) # "22 ( Extra Stuff )"
It is also possible to create a subclass with multiple parents:
class ParentClassOne:
testVariableA = "This is another test. In fact, this is the last one."
class ParentClassTwo:
testVariableB = "Caffeine fuels the world."
def testMethodA ( self ):
return True
class ParentClassThree:
def testMethodB ( self ):
return False
class ChildClass ( ParentClassOne, ParentClassTwo, ParentClassThree ):
pass
anObject = ChildClass()
print anObject.testVariableA # "This is another test. In fact, this is the last one."
print anObject.testVariableB # "Caffeine fuels the world."
print anObject.testMethodA() # True
print anObject.testMethodB() # False
Conclusion
As you've witnessed, Python itself is unbelievably object-oriented, and it supports both simple and complex object-oriented design. While scripting in Python, you will come across object orientation regularly. When you create a string, you are creating an object. When you work with files, you are working with objects as well. When you work with Python's extensive standard library, you are, again, working with objects. Objects make Python an incredibly easy language to work with.
You now understand the basics of objects and object-oriented programming. You may now utilize your knowledge in your scripts, potentially simplifying the development process.
| DISCLAIMER: The content provided in this article is not warranted or guaranteed by Developer Shed, Inc. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. As such it is incumbent upon the reader to employ real-world tactics for security and implementation of best practices. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. If this is a hardware review, it is not recommended to open and/or modify your hardware. |
/ 30 
