调用类方法会在Python中引发TypeError [英] Calling a class method raises a TypeError in Python

问题描述

我不明白类的使用方式.当我尝试使用该类时，以下代码给我一个错误.

I don't understand how classes are used. The following code gives me an error when I try to use the class.

class MyStuff:
    def average(a, b, c): # Get the average of three numbers
        result = a + b + c
        result = result / 3
        return result

# Now use the function `average` from the `MyStuff` class
print(MyStuff.average(9, 18, 27))

错误:

File "class.py", line 7, in <module>
    print(MyStuff.average(9, 18, 27))
TypeError: unbound method average() must be called with MyStuff instance as first argument (got int instance instead)

怎么了?

推荐答案

您可以通过声明变量并像调用一个函数一样来实例化该类:

You can instantiate the class by declaring a variable and calling the class as if it were a function:

x = mystuff()
print x.average(9,18,27)

但是，这不适用于您提供给我们的代码.当您在给定对象(x)上调用类方法时，它在调用函数时始终将指向该对象的指针作为第一个参数传递.因此，如果您现在运行代码，则会看到以下错误消息:

However, this won't work with the code you gave us. When you call a class method on a given object (x), it always passes a pointer to the object as the first parameter when it calls the function. So if you run your code right now, you'll see this error message:

TypeError: average() takes exactly 3 arguments (4 given)

要解决此问题，您需要修改平均值方法的定义以采用四个参数.第一个参数是对象引用，其余3个参数将用于3个数字.

To fix this, you'll need to modify the definition of the average method to take four parameters. The first parameter is an object reference, and the remaining 3 parameters would be for the 3 numbers.

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