Python [set()]中的类变量

Question

为什么set对于python中的类变量的行为与字典不同。例如,

class Test1:
   x=set()
   y={}

hamster=Test1()
chinchilla=Test1()
hamster.x.add('hi')  # now both sets in both instances have 'hi'
hamster.y['key']=5   # only the hamster instance will contain 5

(谢谢你的帮助:)

编辑:我还注意到，如果在self.x=set init()中定义()，可以避免向这两个实例添加的问题。删除了打印

Answer 1

不，你错了，两个都有key:5

In [56]: class Test1:
   ....:        x=set()
   ....:    y={}
   ....: 

In [57]: hamster=Test1()

In [58]: chinchilla=Test1()

In [59]: hamster.x.add('hi')  # now both sets in both instances have 'hi'

In [60]: hamster.y['key']=5

In [62]: hamster.x,chinchilla.x
Out[62]: (set(['hi']), set(['hi']))

In [63]: hamster.y,chinchilla.y
Out[63]: ({'key': 5}, {'key': 5})

实际上，在代码中，您不是在更改实例变量，而是在更改类变量：

In [65]: Test1.x
Out[65]: set(['hi'])

In [66]: Test1.y
Out[66]: {'key': 5}

您需要在这里使用实例变量：

In [71]: class Test1():
    def __init__(self):
        self.x=set()
        self.y={}
   ....:         
   ....:         

In [75]: hamster=Test1()

In [76]: chinchilla=Test1()

In [77]: hamster.x.add('hi')

In [78]: chinchilla.x.add('bye')

In [79]: hamster.x
Out[79]: set(['hi'])

In [81]: chinchilla.x
Out[81]: set(['bye'])


In [82]: hamster.y['key']=5

In [83]: hamster.y,chinchilla.y
Out[83]: ({'key': 5}, {})