Python:使类可迭代 [英] Python: Make class iterable

问题描述

我继承了一个包含许多大类的项目，这些大类仅由类对象(整数，字符串等)组成.我希望能够检查是否存在属性，而无需手动定义属性列表.

I have inherited a project with many large classes constituent of nothing but class objects (integers, strings, etc). I'd like to be able to check if an attribute is present without needed to define a list of attributes manually.

是否可以使用标准语法使其本身可迭代的python class ?也就是说，我希望能够使用for attr in Foo:(甚至是if attr in Foo)对类的所有属性进行迭代，而无需首先创建类的实例.我想我可以通过定义__iter__来做到这一点，但是到目前为止，我还没有完全找到想要的东西.

Is it possible to make a python class iterable itself using the standard syntax? That is, I'd like to be able to iterate over all of a class's attributes using for attr in Foo: (or even if attr in Foo) without needing to create an instance of the class first. I think I can do this by defining __iter__, but so far I haven't quite managed what I'm looking for.

通过添加这样的__iter__方法已经实现了我想要的一些东西:

I've achieved some of what I want by adding an __iter__ method like so:

class Foo:
    bar = "bar"
    baz = 1
    @staticmethod
    def __iter__():
        return iter([attr for attr in dir(Foo) if attr[:2] != "__"])

但是，这并不能完全满足我的需求:

However, this does not quite accomplish what I'm looking for:

>>> for x in Foo:
...     print(x)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'classobj' object is not iterable

即使如此，这仍然可行:

Even so, this works:

>>> for x in Foo.__iter__():
...     print(x)
bar
baz

推荐答案

将__iter__添加到元类而不是类本身(假设Python 2.x):

Add the __iter__ to the metaclass instead of the class itself (assuming Python 2.x):

class Foo(object):
    bar = "bar"
    baz = 1
    class __metaclass__(type):
        def __iter__(self):
            for attr in dir(self):
                if not attr.startswith("__"):
                    yield attr

对于Python 3.x，使用

For Python 3.x, use

class MetaFoo(type):
    def __iter__(self):
        for attr in dir(self):
            if not attr.startswith("__"):
                yield attr

class Foo(metaclass=MetaFoo):
    bar = "bar"
    baz = 1

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