从单独文件中的类创建对象

问题描述

我已经完成了几个关于 Python 的教程，并且我知道如何定义类，但我不知道如何使用它们.例如，我创建了以下 file (car.py):

I have done several tutorials on Python and I know how to define classes, but I don't know how to use them. For example I create the following file (car.py):

class Car(object):
    condition = 'New'
    def __init__(self,brand,model,color):
        self.brand = brand
        self.model = model
        self.color = color

    def drive(self):
        self.condition = 'Used'

然后我创建另一个文件 (Mercedes.py)，我想从 Car 类中创建一个对象 Mercedes:

Then I create another file (Mercedes.py), where I want to create an object Mercedes from the class Car:

Mercedes = Car('Mercedes', 'S Class', 'Red')

，但我得到一个错误:

NameError: name 'Car' is not defined

如果我在创建实例(汽车)的同一个文件中创建实例(对象)，我没有问题:

If I create an instance (object) in the same file where I created it (car), I have no problems:

class Car(object):
    condition = 'New'
    def __init__(self,brand,model,color):
        self.brand = brand
        self.model = model
        self.color = color

    def drive(self):
        self.condition = 'Used'

Mercedes = Car('Mercedes', 'S Class', 'Red')

print (Mercedes.color)

哪些打印:

Red

所以问题是:如何从同一个包(文件夹)中不同文件的类创建对象?

So the question is: How can I create an object from a class from different file in the same package (folder)?

推荐答案

在你的 Mercedes.py 中，你应该按如下方式导入 car.py 文件(只要因为这两个文件在同一个目录):

In your Mercedes.py, you should import the car.py file as follows (as long as the two files are in the same directory):

import car

那么你可以这样做:

Mercedes = car.Car('Mercedes', 'S Class', 'Red')  #note the necessary 'car.'

或者，你可以这样做

from car import Car

Mercedes = Car('Mercedes', 'S Class', 'Red')      #no need of 'car.' anymore

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