I’m YouKoutaku. These codes are from the book python_Crash_Course, 2nd edition. I learned python and took these notes for this book.
9. Class
9.1 create and use class
9.1.1 create a class
class_name must be capital.
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| class Dog:
"""dog class"""
def __init__(self, name, age):
"""setup for name and age"""
self.name = name
self.age = age
def sit(self):
"""dog sit"""
print(f"{self.name} is now sitting.")
def roll_over(self):
""""""
print(f"{self.name} rolled over!")
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The function in class is called method.
_init_(self, parameter_name, ...)
The self must be the frist argument. self can used by all methods in class. another parameter. self.parameter_name is called properties.
9.1.2 create a instance
- using the properties of class
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| class Dog:
"""dog class"""
def __init__(self, name, age):
"""setup for name and age"""
self.name = name
self.age = age
def sit(self):
"""dog sit"""
print(f"{self.name} is now sitting.")
def roll_over(self):
""""""
print(f"{self.name} rolled over!")
my_dog = Dog('Willie', 6)
print(f"My dog's name is {my_dog.name}.")
print(f"My dog is {my_dog.age} years old.")
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| My dog's name is Willie.
My dog is 6 years old.
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- using the methods of class
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| class Dog:
"""dog class"""
def __init__(self, name, age):
"""setup for name and age"""
self.name = name
self.age = age
def sit(self):
"""dog sit"""
print(f"{self.name} is now sitting.")
def roll_over(self):
""""""
print(f"{self.name} rolled over!")
my_dog = Dog('Willie', 6)
my_dog.sit()
my_dog.roll_over()
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| Willie is now sitting.
Willie rolled over!
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- more instance used class
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| class Dog:
"""dog class"""
def __init__(self, name, age):
"""setup for name and age"""
self.name = name
self.age = age
def sit(self):
"""dog sit"""
print(f"{self.name} is now sitting.")
def roll_over(self):
""""""
print(f"{self.name} rolled over!")
my_dog = Dog('Willie', 6)
your_dog = Dog('Lucy',3)
my_dog.sit()
your_dog.roll_over()
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| Willie is now sitting.
Lucy rolled over!
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9.2 using class and instance
9.2.1 a sample class
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| class Car:
"""simulation for car"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
def get_descriptive_name(self):
"""return info"""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
my_new_car = Car('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
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9.2.2 default values for properties
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| class Car:
"""simulation for car"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""return info"""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
print(f"This car has {self.odometer_reading} miles on it.")
my_new_car = Car('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
my_new_car.read_odometer()
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| 2019 Audi A4
This car has 0 miles on it.
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9.2.3. change values of properties
- Directly
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| class Car:
"""simulation for car"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""return info"""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
print(f"This car has {self.odometer_reading} miles on it.")
my_new_car = Car('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
my_new_car.odometer_reading = 23
my_new_car.read_odometer()
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| 2019 Audi A4
This car has 23 miles on it.
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- by method
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| class Car:
"""simulation for car"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""return info"""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
print(f"This car has {self.odometer_reading} miles on it.")
def update_odometer(self, mileage):
"""change the odometer value"""
self.odometer_reading = mileage
my_new_car = Car('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
my_new_car.update_odometer(23)
my_new_car.read_odometer()
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| 2019 Audi A4
This car has 23 miles on it.
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| #app extra work
class Car:
"""simulation for car"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""return info"""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
print(f"This car has {self.odometer_reading} miles on it.")
def update_odometer(self, mileage):
"""change the odometer value and """
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print("You can't roll back an odometer!")
my_new_car = Car('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
my_new_car.update_odometer(23)
my_new_car.read_odometer()
my_new_car.update_odometer(13)
my_new_car.read_odometer()
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| 2019 Audi A4
This car has 23 miles on it.
You can't roll back an odometer!
This car has 23 miles on it.
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- increment the value by method
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| class Car:
"""simulation for car"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""return info"""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
print(f"This car has {self.odometer_reading} miles on it.")
def update_odometer(self, mileage):
"""change the odometer value and """
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print("You can't roll back an odometer!")
def increment_odometer(self, miles):
"""increment the value to odometer"""
self.odometer_reading += miles
my_new_car = Car('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
my_new_car.update_odometer(23_500)
my_new_car.read_odometer()
my_new_car.increment_odometer(1000)
my_new_car.read_odometer()
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| 2019 Audi A4
This car has 23500 miles on it.
This car has 24500 miles on it.
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9.3 Inheritance
child class can get all methods and properties of parent class.
class child_class_name (parent_class)
9.3.1 _init_() in child class
usually, _init_() of the child clsss need info from _init_() of the parent clsss
super()._init_(parameter_name, ...) is a method to define all properties and methods from parent class. The parent class also is called supercalss, so uesd super.
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| class Car:
"""simulation for car"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""return info"""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
print(f"This car has {self.odometer_reading} miles on it.")
def update_odometer(self, mileage):
"""change the odometer value and """
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print("You can't roll back an odometer!")
def increment_odometer(self, miles):
"""increment the value to odometer"""
self.odometer_reading += miles
class ElectricCar(Car):
def __init__(self, make, model, year):
"""add parent class's properties and methods"""
super().__init__(make, model, year)
my_new_car = ElectricCar('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
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9.3.2 add the properties and methods for child class
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| class Car:
"""simulation for car"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""return info"""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
print(f"This car has {self.odometer_reading} miles on it.")
def update_odometer(self, mileage):
"""change the odometer value and """
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print("You can't roll back an odometer!")
def increment_odometer(self, miles):
"""increment the value to odometer"""
self.odometer_reading += miles
class ElectricCar(Car):
def __init__(self, make, model, year):
"""add parent class's properties and methods"""
super().__init__(make, model, year)
self.battery_size = 75
def describe_battery(self):
"""print the battery info"""
print(f"This car has a {self.battery_size}-kWh battery.")
my_tesla = ElectricCar('tesla', 'model s', 2019)
print(my_tesla.get_descriptive_name())
my_tesla.describe_battery()
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| 2019 Tesla Model S
This car has a 75-kWh batery.
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9.3.3 Rewriting the methoed of parent class
define the same name method again.
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| class Car:
"""simulation for car"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def fill_gas_tank(self):
print("xxxxxx")
class ElectricCar(Car):
def __init__(self, make, model, year):
"""add parent class's properties and methods"""
super().__init__(make, model, year)
self.battery_size = 75
def fill_gas_tank(self):
print("This car doesn't need a gas tank!")
my_tesla = ElectricCar('tesla', 'model s', 2019)
my_tesla.fill_gas_tank()
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| This car doesn't need a gas tank!
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9.3.4 make instence as a properties
The list of properties and methods is longer when the class has more detals. So we can create a sub-instence by class as properties of the main-isntence in _init_().
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| class Car:
"""simulation for car"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""return info"""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
class Battery:
def __init__(self, battery_size=75):
self.battery_size = battery_size
def describe_battery(self):
"""print the battery info"""
print(f"This car has a {self.battery_size}-kWh battery.")
class ElectricCar(Car):
def __init__(self, make, model, year):
"""add parent class's properties and methods"""
super().__init__(make, model, year)
self.battery = Battery()
my_tesla = ElectricCar('tesla', 'model s', 2019)
print(my_tesla.get_descriptive_name())
my_tesla.battery.describe_battery()
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| 2019 Tesla Model S
This car has a 75-kWh batery.
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It seems unnecessary, but this grading method can help us better understand and modify our code.
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| class Car:
"""simulation for car"""
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""return info"""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
class Battery:
def __init__(self, battery_size=75):
self.battery_size = battery_size
def describe_battery(self):
"""print the battery info"""
print(f"This car has a {self.battery_size}-kWh battery.")
def get_range(self):
if self.battery_size == 75:
range = 260
if self.battery_size == 100:
range = 315
print(f"This car can go about {range} miles on a full charge.")
class ElectricCar(Car):
def __init__(self, make, model, year):
"""add parent class's properties and methods"""
super().__init__(make, model, year)
self.battery = Battery()
my_car = ElectricCar('tesla', 'model s', 2019)
print(my_car.get_descriptive_name())
my_car.battery.describe_battery()
my_car.battery.get_range()
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| 2019 Tesla Model S
This car has a 75-kWh batery.
This car can go about 260 miles on a full charge.
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9.4 import class
9.4.1 import a single class
from file_name import class_name
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| from car import Car
my_car = Car('tesla', 'model s', 2019)
print(my_car.get_descriptive_name())
my_car.update_odometer(23_500)
my_car.read_odometer()
my_car.increment_odometer(1000)
my_car.read_odometer()
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9.4.2 multiple classes in one module
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| from car import ElectricCar
my_car = ElectricCar('tesla', 'model s', 2019)
print(my_car.get_descriptive_name())
my_car.battery.describe_battery()
my_car.battery.get_range()
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9.4.3 import multiple classes
from file_name import class_name, class_name, xxxx
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| from car import Car, ElectricCar
my_beetle = Car('volkswagen', 'beetle', 2019)
print(my_beetle.get_descriptive_name())
my_tesla = ElectricCar('tesla', 'roadster', 2019)
print(my_tesla.get_descriptive_name())
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9.4.4 import one modules
import module_name
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| import car
my_beetle = car.Car('volkswagen', 'beetle', 2019)
print(my_beetle.get_descriptive_name())
my_tesla = car.ElectricCar('tesla', 'roadster', 2019)
print(my_tesla.get_descriptive_name())
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9.4.5 import all classes in one module
from module_name import *
But this way is not a good. because we can’t know where the class from. And class’s name maybe repeated.
9.4.6 import one module to another module
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| from car import Car
from electric_car import ElectricCar
my_beetle = Car('volkswagen', 'beetle', 2019)
print(my_beetle.get_descriptive_name())
my_tesla = ElectricCar('tesla', 'roadster', 2019)
print(my_tesla.get_descriptive_name())
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9.4.7 rename a class when importing
from module_name import class_name as new_name
9.5 python standard library
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| from random import randint
randint(1, 100)
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| from random import choice
players = ['charles', 'martina', 'michael', 'david']
first_up = choice(players)
print(first_up)
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