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Oct 12, 2015 · Again, there are several reasons not to use OOP, and you don't need to. But luckily with a language like Python, you can use just a little bit or a lot, it's up to you. An example of the student use case (no guarantee on code quality, just an example): Object Oriented
• A class is a special data type which defines how to build a certain kind of object. • The class also stores some data items that are shared by all the instances of this class • Instances are objects that are created which follow the definition given inside of the class • Python doesn’t use separate class interface
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Classes in Python – An Introduction Though not always explicitly stated, Python provides several types of variables to store data in: int, float, boolean and string. However, not all information can be easily stored in one of these types. One solution that we’ve seen is using a list. A list can store an arbitrary amount of information.
- Topics
- What are objects
- Design of Circle object
- Design of Circle
- Circle: classes and objects
- To get an instance variable from an object, use: < >.variable
- Attributes / Instance Variables
- Messages
- Message Passing
- Why use classes at all?
- Encapsulation
- abstraction:
- Hiding your private parts (in Python)
- Getters and Setters (or) Accessors and Mutators
- • Definition of my getter:
- Getters and Setters
- Helping other people use your classes
- Putting Classes in Modules
- Module Documentation
- PyDoc
Objects and Classes Abstraction Encapsulation Messages
An object is a datatype that stores data, but ALSO has operations defined to act on the data. It knows stuff and can do stuff. Generally represent: tangible entities (e.g., student, airline ticket, etc.) intangible entities (e.g., data stream) Interactions between objects define the system operation (through message passing) What are Objects ...
A Circle object: center, which remembers the center point of the circle, radius, which stores the length of the circle’s radius. color, which stores the color The draw method examines the center and radius to decide which pixels in a window should be colored. The move method sets the center to another location, and redraws the circle
All objects are said to be an instance of some class. The class of an object determines which attributes the object will have. A class is a description of what its instances will know and do.
Classes are blueprints or directions on how to create an object
What happens if the instance variable doesn’t exist?
Attributes represent the characteristics of a class. When an object is instantiated and the values are assigned to attributes, they are then referred to as instance variables. The values of the instance variables define the state of the individual object They are referred to as instance variables because the values assigned to an individual obj...
Process by which system components interact: send data to another object request data from another object request object to perrform some behavior Implemented as methods (not called functions). Functions are procsses that are object independet Methods are dependent on the state of the object
When calling a method in another class, OO uses the term “message passing” you are passing messages from one class to another Don’t be confused... this is really just a new name for calling a method or a function
Classes and objects are more like the real world. They minimize the semantic gap by modeling the real world more closely The semantic gap is the difference between the real world and the representation in a computer. Do you care how your TV works? No... you are a user of the TV, the TV has operations and they work. You don’t care how. Why use class...
Attributes and behaviors are enclosed (encapsulated) within the logical boundary of the object entity In structured or procedural systems, data and code are typically maintained as separate entities (e.g., modules and data files) In Object Technology systems, each object contains the data (attributes) and the code (behaviors) that operates upon...
details associated with object sub-components are enclosed within the logical boundary of the object user of object only “sees” the public interface of the object, all the internal details are hidden Note - In Python, encapsulation is merely a programming convention. Other languages (e.g., Java) enforce the concept more rigorously. Abstraction ...
• You can create somewhat private parts in Python. Naming an instance variable with an __ (two underscores) makes it private. Hiding your private parts (in Python) • Be a little sneakier then.. use __name: Nice try, but that won’t work! Hiding your private parts (in Python) • Be super sneaky then.. use _Student__name: Ahh... you saw my private part...
These methods are a coding convetion Getters/Accessors are methods that return an attribute def get_name(self): Setters/Mutators are methods that set an attribute def set_name(self,newName):
def getName(self): return self.name What if I want to store the name instead as first and last name in the class? Well, with the getter I only have to do this: def getName(self): return self.firstname + self.lastname If I had used dot notation outside the class, then all the code OUTSIDE the class would need to be changed because the internal struc...
• Getters and setters are useful to provide data encapsulation. They hide the internal structure of your class and they should be used!
Frequently, you will need to write classes other people will use Or classes you will want to use later, but have forgotton how Answer: Document your class usage!
Sometimes we may program a class that could useful in many other programs. If you might be reusing the code again, put it into its own module file with documentation to describe how the class can be used so that you won’t have to try to figure it out in the future from looking at the code!
You are already familiar with “#” to indicate comments explaining what’s going on in a Python file. Python also has a special kind of commenting convention called the docstring. You can insert a plain string literal as the first line of a module, class, or function to document that component. Module Documentation Why use a docstring? Ordinary comme...
PyDoc The pydoc module automatically generates documentation from Python modules. The documentation can be presented as pages of text on the console, served to a Web browser, or saved to HTML files. pydoc –g # Launch the GUI
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Classes in Python Python contains a class creation mechanism that’s fairly similar to what’s found in C++ or Java. There are significant differences though: • All class members are public. • Instance fields aren’t declared. Rather, you just create fields as needed by assignment (often in constructors). • There are class fields ...
Python classes (1) Similar class concept as in Java and C++ All functions are virtual No private/protected variables (the effect can be "simulated") Single and multiple inheritance Remember; everything in Python is an object (even a class) Python classes revisited – p.19/32
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1.1 Classes From the OOP perspective, classes describe objects, and each object is an instance of a class. The class statement allow us to define a class. For convention, we name classes using CamelCase and methods using snake_case. Here is an example of a class in Python: 1 # create_apartment.py 2 3 4 class Apartment: 5 '''
