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python:python_misc:oo_fundamentals_with_python [2018/08/20 20:15] – ↷ Page name changed from python:python_misc:python_oo_fundamentals to python:python_misc:oo_fundamentals_with_python mithatpython:python_misc:oo_fundamentals_with_python [2018/11/30 18:45] (current) – [Instantiation and use] mithat
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 ===== What you'll need to know ===== ===== What you'll need to know =====
-In what follows, we assume know basic Python programming concepts including:+In what follows, we assume you know basic Python programming concepts including:
  
   * How to create and use variables.   * How to create and use variables.
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 ==== Behavior ==== ==== Behavior ====
  
-A given microwave oven also has predefined **behavior**.+A given microwave oven also has predefined **behavior**:
  
   * //Push the "1" button// → start cooking at maximum power for one minute.   * //Push the "1" button// → start cooking at maximum power for one minute.
-  * //Push the "+30sec" button// → add 30 seconds to the cooking time if it's already cooking or start cooking for 30 seconds at maximum power otherwise.+  * //Push the "+30sec" button// → start cooking for 30 seconds at maximum power or add 30 seconds to the cooking time if it's already cooking.
   * //Push a magical combination of buttons// → set the internal clock.   * //Push a magical combination of buttons// → set the internal clock.
   * And so on.   * And so on.
  
-These operations are one that happen to be public-facing (i.e., operations a user can engage). There might very well also be operations that go on inside the oven to support the oven's functioning that the user will never be aware of. All these operations collectively define the oven's behavior. We call the public-facing behavior (i.e., the operations a user can engage) the oven's **interface**.+These operations are ones that happen to be public-facing (i.e., operations a user can engage). There might very well also be operations that go on inside the oven that the user will never be aware of to support the oven's functioning. We call the //public-facing behavior// (i.e., the operations a user can engage) the oven's **interface**.
  
 ====  Encapsulation and protection ==== ====  Encapsulation and protection ====
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 {{:python:about_python:farberware4241-200.jpeg?nolink|}} {{:python:about_python:farberware4241-200.jpeg?nolink|}}
  
-I have a Farberware 4241 microwave oven in my office. It's small, but it gets the job done. There is a factory somewhere making these by the thousand million. They make all the Farberware 4241s from a master plan. That master plan defines what the Farberware 4241 //is//. In computing terminology, we would call that master plan a **class**. A class contains all the specifications needed to make a particular kind of object. +I have a Farberware 4241 microwave oven in my office. It's small, but it gets the job done. There is a factory somewhere making these by the thousand million. They make all the Farberware 4241s from a master plan, a plan that defines what the Farberware 4241 //is//. In object-oriented design terminology, we would call that master plan a **class**. A class contains all the specifications needed to make a particular kind of object.
  
-Every Farberware 4241 begins its life identical to every other freshly-made Farberware 4241 because they were made using the same master plan. So, the one in my office that I pulled out of the box last month was identical to the one that I bought my best friend last week later because they were built from the same master plan, or, if you will, the same class. But as my best friend and I started using our ovens, the state of each changed. Note that while the behavior designed into the oven---the operations it's capable of---doesn't (and won't) change, the state of any individual oven does change over time.+Languages that support **class-based object-oriented programming** let you define classes at a very high level. Once you've defined a class you can then create **instances**: objects created from a class. The process of creating an instance from a class is called **instantiation**.
  
-In **class-based object-oriented programming**, we call objects that have been created from classes **instances**. Thus my oven is an instance of a Farberware 4241. The process of creating an instance from a class is called **instantiation**. So you might say the Farberware factory spends it's entire day instantiating 4241 ovens.+Thus my oven is an instance of a Farberware 4241, and you might say the Farberware factory spends it's entire day instantiating 4241 ovens.
  
 ==== Prototype-based object-orientation ==== ==== Prototype-based object-orientation ====
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 )) \\ {{..:about_python:tottycounter.jpg?234|}} )) \\ {{..:about_python:tottycounter.jpg?234|}}
  
-In case you've never seen this bit of advanced technology before, it's a clicker-counter or tally-counter. It has two controls: a button you click to advance the counter by one and another you press to reset the count to zero. Our goal is to build one of these in software using object-orientation.+In case you've never seen one of these bits of advanced technology before, it's a clicker-counter or tally-counter. It has two controls: a button you click to advance the counter by one and another you press to reset the count to zero. Our goal is to build one of these in software using object-orientation.
  
 One way to start building a model for a class is to start listing the public-facing behavior (or the //interface//) you want an object of that class to have. A pretty comprehensive list of the things you might do with a clicker-counter is: One way to start building a model for a class is to start listing the public-facing behavior (or the //interface//) you want an object of that class to have. A pretty comprehensive list of the things you might do with a clicker-counter is:
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   * //reset//: sets the count to zero.   * //reset//: sets the count to zero.
  
-Next we can think about what data we'll need to keep track of the state of a clicker-counter. In this case, it's pretty simple: all we really need is one integer to store the count value.+Next we can think about what data we'll need to keep track of the state of a clicker-counter. In this case, it's pretty simple: all we really need is one integer to store the //count// value.
  
 So, a summary of what we need so far is: So, a summary of what we need so far is:
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   * a //click// operation   * a //click// operation
   * a //reset// operation   * a //reset// operation
-  * an integer to store the count+  * an integer to store the //count//
  
 In Python, object **attributes**, which together make up the state, are defined in special variables called **instance variables**. A class definition can include as many instance variables as it needs to store the state. In our case, we are getting off easy: the clicker-counter only needs one. The **operations** our object will be capable of, which make up behavior, are defined using **instance methods**. In Python a method is nothing more than a function defined inside a class. We call anything belonging to a class (e.g., instance variables and methods) a **member** of the class. In Python, object **attributes**, which together make up the state, are defined in special variables called **instance variables**. A class definition can include as many instance variables as it needs to store the state. In our case, we are getting off easy: the clicker-counter only needs one. The **operations** our object will be capable of, which make up behavior, are defined using **instance methods**. In Python a method is nothing more than a function defined inside a class. We call anything belonging to a class (e.g., instance variables and methods) a **member** of the class.
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 </code> </code>
  
-Class definitions follow the same header/suite pattern for compound statements you've seen before with control flow statements and function definitions. The keyword ''class'' in the header declares that what follows is a class definition. The 'ClickerCounter' identifier is the name of our class. And the parenthesis are there for implementing an advanced feature that we'll not tackle here.+Class definitions follow the same header/suite pattern for compound statements you've seen before with control flow statements and function definitions. The keyword ''class'' in the header declares that what follows is a class definition. The ''ClickerCounter'' identifier is the name of our class. The parenthesis that follow the name of the class are there for implementing an advanced feature that we'll not tackle here.
  
-The suite of the class definition nests additional compound statements, in this case a set of function definitions---the instance methods.+The suite of the class definition nests additional compound statements: function definitions that make up the instance methods.
  
 In this class definition, we define three instance methods: ''%%__init__(self)%%'', ''click(self)'', and ''reset(self)''. These methods will belong to objects created with this class; they won't have any meaning outside of this context. In this class definition, we define three instance methods: ''%%__init__(self)%%'', ''click(self)'', and ''reset(self)''. These methods will belong to objects created with this class; they won't have any meaning outside of this context.
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 <WRAP center round tip 80%> <WRAP center round tip 80%>
-A common error is to forget to use ''self'' as the first parameter in an instance method definition. Another common error is to forget to use ''self'' to qualify the names of instance variables. Things will go wonky if you do either of these.+A common error is to forget to use ''self'' as the first parameter in an instance method definition. Another common error is to forget to use ''self'' to qualify the names of instance variables inside instance methods. Things won't go as expected if you do either of these.
 </WRAP> </WRAP>
  
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 a.click(self) a.click(self)
 </code> </code>
-Python's inner workings manage the fist parameter automatically and implicitly.+Python's inner workings manage the fist parameter (i.e., ''self'') automatically and implicitly.
  
 ==== Parameterized constructors and methods ==== ==== Parameterized constructors and methods ====
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 ==== Next steps ==== ==== Next steps ====
  
-This just scratches the surface of what's possible with object-oriented programming. In particular, we haven't addressed the matter of protecting our class' members. But with even with the basics you have learned here, you can now create Python objects whose state is maintained through predefined behaviors.+This just scratches the surface of what's possible with object-oriented programming. In particular, we haven't addressed the matter of protecting our class' members or reusing code through //inheritance//. But with even with the basics you have learned here, you can now create Python objects whose state is maintained through predefined behaviors.
  
 Copyright © 2011-2018 Mithat Konar. All rights reserved. Copyright © 2011-2018 Mithat Konar. All rights reserved.
python/python_misc/oo_fundamentals_with_python.1534796127.txt.gz · Last modified: 2018/08/20 20:15 by mithat
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