获取所有可能的类属性的完整列表 [英] Get complete list of all possible Class Attributes

问题描述

给定一个简单的Class，是否有一种方法可以输出所有可能的属性? __class__和__doc__ 和 等标准属性特殊只读属性，例如__mro__，__bases__等.通常， 所有 是否显示属性?

Is there a way, given a simple Class, to output all the possible attributes for it? Standard attributes like __class__ and __doc__ and special read only attributes like __mro__, __bases__ et al. Generally, all present attributes?

考虑类的最简单情况:

class myClass:
    pass

dir()，vars()和inspect.getmembers()均排除某些builtin属性.使用myClass.__dir__(MyClass)可以提供最完整的列表，该列表在添加内置属性时会排除用户定义的MyClass属性，例如:

The dir(), vars() and inspect.getmembers() all exclude certain builtin attributes. The most complete list is offered by using myClass.__dir__(MyClass) which, while adding built in attributes, excludes user defined attributes of MyClass, for example:

In [3]: set(MyClass.__dir__(MyClass)) - set(dir(MyClass))
Out[3]: 
{'__abstractmethods__', '__base__', '__bases__',
 '__basicsize__', '__call__', '__dictoffset__',
 '__flags__', '__instancecheck__', '__itemsize__',
 '__mro__', '__name__', '__prepare__', '__qualname__',
 '__subclasscheck__', '__subclasses__', '__text_signature__',
 '__weakrefoffset__', 'mro'}

根据添加的类似问题之一，这是不可能的.如果目前仍无法实现，那么隐藏" 某些属性(如__bases__(从标准调用到dir(), vars() & inspect而不是诸如__name__的那些))背后的原理是什么?

According to one of the added similar questions, this is not possible. If presently still not possible, what is the rationale behind "hiding" certain attributes like __bases__ (from standard calls to dir(), vars() & inspect and not ones like __name__?

• 如何获取对象的方法和属性的完整列表?

这是最有可能被标记为重复的内容， 但是 ，它很旧，并且大多与Python 2.x有关.可以接受的答案是，没有办法，但是它是在08'中提供的. 12'中的最新答案建议dir()用于新样式类.

This is the most likely to be labeled as a duplicate, but, it is old and mostly regarding Python 2.x. The accepted answer is that there isn't a way but it was provided in 08'. The most recent answer in 12' suggests dir() for new style classes.

打印Python类的所有属性

相似的标题，不同的内容.

Similar title, different content.

获取类的属性

提供dir()和inspect解决方案.

获取Python中的所有对象属性?

同样，提出dir().

推荐答案

dir() 基本上是一种方便的方法，它不应该返回所有内容，它的主要作用是递归地返回在类及其基数的字典中找到的所有内容.

dir() is basically a convenience method, it is not supposed to return everything, what it basically does is that it recursively returns everything found in the dictionary of a class and its bases.

PyPy's implementation of dir() is quite easy to understand:

def dir(*args):
    ...
    elif isinstance(obj, (types.TypeType, types.ClassType)):
        # Don't look at __class__, as metaclass methods would be confusing.
        return sorted(_classdir(obj))
    ...

def _classdir(klass):
    """Return a set of the accessible attributes of class/type klass.

    This includes all attributes of klass and all of the base classes
    recursively.
    """
    names = set()
    ns = getattr(klass, '__dict__', None)
    if ns is not None:
        names.update(ns)
    bases = getattr(klass, '__bases__', None)
    if bases is not None:
        # Note that since we are only interested in the keys, the order
        # we merge classes is unimportant
        for base in bases:
            names.update(_classdir(base))
    return names

每个类基本上都继承自object，因此您会看到其中包含一些dunder方法，因为它们实际上是object词典的一部分:

As each class basically inherits from object you will see some dunder methods included because they are actually part of object's dictionary:

>>> class A(object):
    pass
...
>>> set(dir(A)) == set(list(object.__dict__) + list(A.__dict__))
True

---

现在__bases__和其他遗失物品怎么办?

Now what about __bases__ and other missing items?

首先object本身是某物的一个实例，嗯，实际上有点混乱:

First of all object itself is an instance of something, well it's bit of a mess actually:

>>> isinstance(type, object)
True
>>> isinstance(object, type)
True
>>> issubclass(type, object)
True
>>> issubclass(object, type)
False
>>> type.mro(object)
[<type 'object'>]
>>> type.mro(type)
[<type 'type'>, <type 'object'>]

因此，所有__bases__，__ge__等属性实际上都是type的一部分:

So, all of the attributes like __bases__, __ge__ etc are actually part of type:

>>> list(type.__dict__)
['__module__', '__abstractmethods__', '__getattribute__', '__weakrefoffset__', '__dict__', '__lt__', '__init__', '__setattr__', '__subclasses__', '__new__', '__base__', '__mro__', 'mro', '__dictoffset__', '__call__', '__itemsize__', '__ne__', '__instancecheck__', '__subclasscheck__', '__gt__', '__name__', '__eq__', '__basicsize__', '__bases__', '__flags__', '__doc__', '__delattr__', '__le__', '__repr__', '__hash__', '__ge__']

因此，当我们执行A.__bases__时，实际上是在查找

Hence when we do A.__bases__ we are actually looking up a descriptor on type of A, i.e type:

>>> A.__bases__
(<type 'object'>,)
>>> type(A).__dict__['__bases__'].__get__(A, type)
(<type 'object'>,)

因此，由于A是type的实例，所以这些方法不是其自身词典的一部分，而是其类型的词典的一部分.

So, as A is an instance of type these methods are not part of its own dictionary but its type's dictionary.

>> class A(object):
...     spam = 'eggs'
...
>>> a = A()
>>> a.foo = 100
>>> a.bar = 200
>>> a.__dict__
{'foo': 100, 'bar': 200}
>>> A.__dict__
dict_proxy({'__dict__': <attribute '__dict__' of 'A' objects>, '__module__': '__main__', '__weakref__': <attribute '__weakref__' of 'A' objects>, '__doc__': None, 'spam': 'eggs'})

由于type是object的子类，对type的dir()调用将包含object中的某些项目:

As, type is a subclass of object, the dir() call on type will contain some items from object:

>>> set(dir(type)) - set(type.__dict__)
set(['__reduce_ex__', '__str__', '__format__', '__reduce__', '__class__', '__subclasshook__', '__sizeof__'])

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