具有随机属性的Python对象列表

Question

(编辑:randrange只是random.randrange,我没有写自己的RNG)

我正在尝试创建一个我定义的类的实例列表.这是整个班级(按要求):

from random import randrange

class Poly:
    points = [0] * 8
    fill = 'red'
    alpha = 1.0

    def __init__(self, width=100, height=100):
        for i in range(0, 8, 2):
            self.points[i] = randrange(width)
            self.points[i+1] = randrange(height)
        self.alpha = random()
        return

似乎工作正常:

>>> for i in range(5):
        Poly().points

[28, 64, 93, 26, 15, 31, 44, 50]
[24, 14, 47, 14, 35, 17, 63, 62]
[99, 28, 90, 29, 56, 59, 57, 33]
[62, 56, 48, 28, 40, 73, 70, 99]
[99, 32, 27, 99, 42, 57, 86, 12]

但是如果我尝试创建这些对象的列表,我会获得单独的实例(不同的内存地址),但它们都具有相同的随机值:

>>> p = []
>>> for i in range(5):
        p.append(Poly())

>>> p
[<gen_image.Poly instance at 0x02D773C8>, <gen_image.Poly instance at 0x02D77FD0>, <gen_image.Poly instance at 0x0321D030>, <gen_image.Poly instance at 0x02D51E40>, <gen_image.Poly instance at 0x02D51DA0>]

>>> for poly in p:
        print poly.points

[75, 18, 5, 76, 6, 64, 95, 54]
[75, 18, 5, 76, 6, 64, 95, 54]
[75, 18, 5, 76, 6, 64, 95, 54]
[75, 18, 5, 76, 6, 64, 95, 54]
[75, 18, 5, 76, 6, 64, 95, 54]

这里发生了什么？什么是我正在做的事情的正确方法？

Answer 1

将数组的创建移动到__init__方法中.

您正在使用所有对象之间的共享数组.

第一个显示不同的原因是您在构造新的Poly对象之前打印该数组的内容,从而践踏数组内容.如果你保留它们并在以后检查它们,它们看起来都与你生成的最后一个内容相同.

哦,在发布问题时尽量不要简化代码.始终发布完整但简短的程序来重现问题.

这是一个简短但完整的程序,用于演示您遇到的问题:

from random import randrange
class Poly:
    points = [0]*8

    def __init__(self, width=100, height=100):
        for i in range(0, 8, 2):
            self.points[i] = randrange(width)
            self.points[i+1] = randrange(height)
        return

p1 = Poly()
print "p1:", p1.points
p2 = Poly()
print "p2:", p2.points
print "p1:", p1.points

样本输出:

[C:\Temp] test.py
p1: [19, 5, 1, 46, 93, 18, 18, 57]
p2: [92, 71, 42, 84, 54, 29, 27, 71]
p1: [92, 71, 42, 84, 54, 29, 27, 71]

注意p1是如何变化的.

固定代码可以简单如下:

from random import randrange
class Poly:
    def __init__(self, width=100, height=100):
        self.points = [0]*8
        for i in range(0, 8, 2):
            self.points[i] = randrange(width)
            self.points[i+1] = randrange(height)
        return

虽然我更喜欢@Doug在这里发布的附加变体