python - 类型错误 : __init__() takes from 1 to 3 positional arguments but 4 were given

Question

我在 Beginning Python Games Development Second Edition 书中的一个例子中遇到了问题.

它让我使用以下 __init__ 函数设置一个矢量类(Q 末尾的完整代码):

def __init__(self, x=0, y=0):
    self.x = x
    self.y = y

然后它要求我针对它运行这段代码:

from Vector2 import *

A = (10.0, 20,0)
B = (30.0, 35.0)
AB = Vector2.from_points(A, B)
step = AB * .1
position = Vector2(A, B)
step = AB * .1
print(*A)
position = Vector2(*A)
for n in range(10):
    position += step
    print(position)

结果出现如下错误:

Traceback (most recent call last):
  File "C:/Users/Charles Jr/Dropbox/Python/5-14 calculating positions.py", line 10, in <module>
    position = Vector2(*A)
TypeError: __init__() takes from 1 to 3 positional arguments but 4 were given

当我在 *A 上打印时，如您所料，它只有 2 个数字。为什么要以某种方式将其变成 4？

完整的Vector2代码:

import math

class Vector2:

    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y

    def __str__(self):
        return "(%s, %s)"%(self.x, self.y)

    def from_points(P1, P2):
        print("foo")
        return Vector2( P2[0] - P1[0], P2[1] - P1[1])

    def get_magnitude(self):
        return math.sqrt( self.x**2 + self.y**2 )

    def normalise(self):
        magnitude = self.get_magnitude()
        self.x /= magnitude
        self.y /= magnitude

    # rhs stands for right hand side
    def __add__(self, rhs):
        return Vector2(self.x + rhs.x, self.y + rhs.y)

    def __sub__(self, rhs):
        return Vector2(self.x - rhs.x, self.y - rhs.y)

    def __neg__(self):
        return Vector2(-self.x, -self.y)

    def __mul__(self, scalar):
        return Vector2(self.x * scalar, self.y * scalar)

    def __truediv__(self, scalar):
        return Vector2(self.x / scalar, self.y / scalar)

Answer 1

A 包含三个 元素，(10.0, 20, 0)，因为您使用了逗号，而不是 。 定义时的小数点:

A = (10.0, 20,0)
#            ^ that's a comma

与 self 参数一起表示您将 4 个参数传递给 __init__ 方法。