Python在循环中创建类实例 [英] Python creating class instances in a loop

问题描述

我是python的新手，所以现在我很困惑.我只想在一个循环中创建几个MyClass类的实例.

I'm new to python, so I'm pretty confused now. I just want to create a couple of instances of class MyClass in a loop.

我的代码:

for i in range(1, 10):
  my_class = MyClass()
  print "i = %d, items = %d" % (i, my_class.getItemsCount());
  my_class.addItem(i)

MyClass类

class MyClass:

  __items = []

  def addItem(self, item):
    self.__items.append(item)

  def getItemsCount(self):
    return self.__items.__len__();

输出为:

i = 0, items = 0
i = 1, items = 1
i = 2, items = 2
and so on...

但是我希望每次迭代都在变量my_class中添加MyClass的新空实例.所以预期的输出是:

But I expect new empty instance of MyClass in variable my_class on each iteration. So expected output is:

i = 0, items = 0
i = 1, items = 0
i = 2, items = 0

您能帮助我理解吗? 谢谢.

Could you help me with understanding? Thanks.

推荐答案

_items是一个类属性，在类定义期间进行了初始化，因此通过向其添加值来修改类 >属性和非实例属性.

_items is a class attribute, initialized during the class definition, so by appending values to it, you're modifying the class attribute and not instance attribute.

要解决此问题，可以通过将以下代码放入__init__方法中，为该类的每个实例创建_items:

To fight the problem you can create _items for each instance of the class by putting this code into __init__ method:

class MyClass:
    def __init__(self):
        self._items = []

然后_items列表对象在所有类实例中都将有所不同

Then _items list object will be different across all class instances

>>> first = MyClass()
>>> first._items.append(1)
>>> second = MyClass()
>>> second._items.append(1)
>>> first._items is second._items
False

，因此追加将按预期工作.

and therefore appending will work as expected.

顺便说一句，在您的情况下 <对于类变量，c4>不是很好的名称选择.

Btw, in your case __items is not quite good name choice for a class variable.

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