134 lines
3.7 KiB
Markdown
134 lines
3.7 KiB
Markdown
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# Chapter 9. Classes
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Objectives:
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* Making an object from a class is called **instantiation**, and you work with **instances of a class**.
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* In this chapter you’ll write classes and create instances of those classes.
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* You’ll specify the kind of information that can be stored in instances, and you’ll define actions that can be taken with these instances.
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* You’ll also write classes that extend the functionality of existing classes, so similar classes can share code efficiently.
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* You’ll store your classes in modules and import classes written by other programmers into your own program files.
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## Creating and using a class
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```python
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class Dog:
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"""A Simple attempt to model a dog"""
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def __init__(self, name, age):
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"""Initialize name and age attributes."""
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self.name = name
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self.age = age
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def sit(self):
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"""Simulate a dog sitting in response to a command."""
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print(f"{self.name} is now sitting.")
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def roll_over(self):
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"""Simulate rolling over in response to a command"""
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print(f"{self.name} rolled over!")
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```
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### __init__() method
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* A special method python run automatically whenever we create a new instance.
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* `self` in parameters is required in method definition, always come first
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* So method call will automatically pass the `self` argument, it's a reference to itself.
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### Making an Instance from a Class
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```python
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my_dog = Dog('Willie', 6)
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(f"My dog's name is {my_dog.name}.")
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print(f"My dog is {my_dog.age} years old.")
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```
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### Accessing Attributes
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```python
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my_dog.name
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```
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### Calling Methods
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```python
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class Dog:
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--snip--
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my_dog = Dog('Willie', 6)
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my_dog.sit()
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my_dog.roll_over()
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```
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### Creating Multiple Instances
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```python
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class Dog:
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--snip--
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my_dog = Dog('Willie', 6)
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your_dog = Dog('Lucy', 3)
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print(f"My dog's name is {my_dog.name}.")
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print(f"My dog is {my_dog.age} years old.")
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my_dog.sit()
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print(f"\nYour dog's name is {your_dog.name}.")
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print(f"Your dog is {your_dog.age} years old.")
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your_dog.sit();
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```
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## Working with Classes and Instances
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After we create class, we can edit object
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* need write **getter/setter functions** to access attributes
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* may need default value for attribute
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```python
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class Car:
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"""A simple attempt to represent a car."""
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def __init__(self, make, model, year):
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"""Initialize attributes to describe a car."""
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self.make = make
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self.model = model
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self.year = year
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self.odometer_reading = 0
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def get_descriptive_name(self):
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"""Return a neatly formatted descriptive name."""
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long_name = f"{self.year} {self.make} {self.model}"
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return long_name.title()
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def read_odometer(self):
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"""Print a statement showing the car's mileage."""
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print(f"This car has {self.odometer_reading} miles on it.")
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def update_odometer(self, mileage):
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"""Set the odometer reading to the given value."""
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self.odometer_reading = mileage
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my_new_car = Car('audi', 'a4', 2019)
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print(my_new_car.get_descriptive_name())
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my_new_car.update_odometer(23)
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my_new_car.read_odometer()
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```
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* `get_descriptive_name()` is a getter function, so we can get private attributes
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* `odometer_reading` has default value as 0
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## Inheritance
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Use **inheritance** when the class is a specialized version of another class.
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* When one class *inherits* from another, it takes on the attributes and methods of the first class.
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* Original class is called **parent class**, New class is called **child class**
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* Child class can define new attributes/methods
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### __init__() for a Child Class
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Creating a `__init__()` of a child class:
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1. Call `__init__()` from parent class, to initialize parent's attributes
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2.
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