Python- Day 31- CLASSES-Importing Classes

Importing a Single Class from a Module

Keep files organized and uncluttered by placing classes in separate modules.

Example: Create a car.py file for the Car class.

# car.py
#A class that can be used to represent a car.

class Car:
   #A simple attempt to represent a 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):
        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.")

Import and use the Car class in my_car.py

# my_car.py
from car import Car

my_new_car = Car('audi', 'a4', 2024)
print(my_new_car.get_descriptive_name())
my_new_car.odometer_reading = 23
my_new_car.read_odometer()


>>

2024 Audi A4
This car has 23 miles on it.

Storing Multiple Classes in a Module:

Group-related classes within the same module for better organization.

Example: In car.py, add Battery and ElectricCar classes, which are related to Car

# car.py
#A set of classes used to represent gas and electric cars.

class Car:  # Car class definition as above

class Battery:
    #A simple attempt to model a battery for an electric car.

    def __init__(self, battery_size=40):
        self.battery_size = battery_size

    def describe_battery(self):
        print(f"This car has a {self.battery_size}-kWh battery.")

    def get_range(self):
        range = 150 if self.battery_size == 40 else 225
        print(f"This car can go about {range} miles on a full charge.")

class ElectricCar(Car):
    #Models aspects of a car, specific to electric vehicles.

    def __init__(self, make, model, year):
        super().__init__(make, model, year)
        self.battery = Battery()

In my_electric_car.py, import ElectricCar

# my_electric_car.py
from car import ElectricCar

my_leaf = ElectricCar('nissan', 'leaf', 2024)
print(my_leaf.get_descriptive_name())
my_leaf.battery.describe_battery()
my_leaf.battery.get_range()

>>

2024 Nissan Leaf
This car has a 40-kWh battery.
This car can go about 150 miles on a full charge.

Importing Multiple Classes from a Module:

Import several classes at once from a module when using multiple classes from the same module.

# my_cars.py
from car import Car, ElectricCar

my_mustang = Car('ford', 'mustang', 2024)
print(my_mustang.get_descriptive_name())

my_leaf = ElectricCar('nissan', 'leaf', 2024)
print(my_leaf.get_descriptive_name())

>>

2024 Ford Mustang
2024 Nissan Leaf

Importing an Entire Module:

Import the entire module and access classes with dot notation to avoid naming conflicts.

# my_cars.py
import car

my_mustang = car.Car('ford', 'mustang', 2024)
print(my_mustang.get_descriptive_name())

my_leaf = car.ElectricCar('nissan', 'leaf', 2024)
print(my_leaf.get_descriptive_name())

>>

2024 Ford Mustang
2024 Nissan Leaf

Importing All Classes from a Module Using Wildcard:

Syntax:

from module_name import *

Note: Avoid using * as it can cause naming conflicts and reduce code readability.

Importing a Module into Another Module:

Spread classes across modules for large projects, allowing one module to access classes from another.

Example: Store Car in car.py and ElectricCar and Battery in electric_car.py.

# car.py
#A class that can be used to represent a car.

class Car:
    # Car class definition

# electric_car.py
#A set of classes for electric cars.
from car import Car

class Battery:
    # Battery class definition

class ElectricCar(Car):
    # ElectricCar class definition

Import both modules into my_cars.py

# my_cars.py
from car import Car
from electric_car import ElectricCar

my_mustang = Car('ford', 'mustang', 2024)
print(my_mustang.get_descriptive_name())

my_leaf = ElectricCar('nissan', 'leaf', 2024)
print(my_leaf.get_descriptive_name())

Using Aliases for Classes and Modules:

Simplify long class or module names by assigning shorter aliases.

# my_cars.py
from electric_car import ElectricCar as EC

my_leaf = EC('nissan', 'leaf', 2024)
print(my_leaf.get_descriptive_name())

# Using a module alias
import electric_car as ec

my_leaf = ec.ElectricCar('nissan', 'leaf', 2024)

Tip: Bgin with simple structures in one file, and as your code grows, move classes into modules for better organization.

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