对象创建

Question

这只是为了“学习的乐趣”。我完全是从书籍和教程中自学的，而且对编程还是很陌生。我正在尝试探索从列表中创建对象的概念。这是我所拥有的：

class Obj:   # Creates my objects
    def __init__(self, x):
        self.name = x
        print('You have created a new object:', self.name)

objList = []
choice = 'y'

while choice != 'n':   # Loop that runs until user chooses, 'n' to quit
    for i in objList:
        print(i)   # Iterates through the list showing all of the objects added
    for i in objList:
        if Obj(i):
            print(i, 'has already been created.')   # Checks for existance of object, if so skips creation
        else:
            createObj = Obj(i)   # Creates object if it doesn't exist
    choice = input('Add object? (y / n): ')
    if choice == 'y':
        newObject = input('Name of object to add: ')
        if newObject in objList:   # Checks for existance of user enrty in list
            print(newObject, 'already exists.')   # Skips .append if item already in list
        else:
            objList.append(newObject)   # Adds entry if not already in list

print('Goodbye!')

当我运行它时，我得到：

Add object? (y / n): y
Name of object to add: apple
apple
You have created a new object: apple   # At this point, everything is correct
apple has already been created.   # Why is it giving me both conditions for my "if" statement?
Add object? (y / n): y
Name of object to add: pear
apple
pear
You have created a new object: apple   # Was not intending to re-create this object
apple has already been created.
You have created a new object: pear   # Only this one should be created at this point
pear has already been created.   # Huh???
Add object? (y / n): n
Goodbye!

我已经进行了一些研究并阅读了几篇关于创建 dict 来完成我正在尝试做的事情的 cmets。我已经构建了一个使用 dict 执行此操作的程序，但出于学习目的，我试图了解这是否可以通过创建对象来完成。似乎一切正常，除了程序通过遍历列表来检查对象是否存在时，它会失败。

然后我这样做了：

>>> Obj('dog')
You have created a new object: dog
<__main__.Obj object at 0x02F54B50>
>>> if Obj('dog'):
    print('exists')

You have created a new object: dog
exists

这让我想到了一个理论。当我输入“if”语句时，它是否创建了一个名为“dog”的对象的新实例？如果是这样，我如何检查对象的存在？如果我将对象存储在变量中，我顶部 sn-p 的循环不会在每次迭代时覆盖变量吗？我的“打印”语句是因为对象存在还是因为它的下一行代码而运行？抱歉我的问题太长了，但如果我提供更好的信息，我相信我可以得到更好的答案。

Answer 1

对象只是数据和函数的容器。尽管Obj("dog") 和Obj("dog") 是等价的，但它们并不相同。换句话说，每次您拨打__init__ 时，您都会获得一份全新的副本。所有不是None、0 或False 的对象都评估为True，因此您的if 语句成功。

您仍然必须使用字典来查看您过去是否创建过狗。例如，

objects = { "dog" : Obj("dog"), "cat" : Obj("cat") }
if "cat" in objects:
    print objects["cat"].x  # prints cat