是否有一种方法可以获取类实例上存在的属性列表?

class new_class():
    def __init__(self, number):
        self.multi = int(number) * 2
        self.str = str(number)

a = new_class(2)
print(', '.join(a.SOMETHING))

期望的结果是输出"multi, str"。我希望它能看到脚本各个部分的当前属性。


当前回答

>>> class new_class():
...   def __init__(self, number):
...     self.multi = int(number) * 2
...     self.str = str(number)
... 
>>> a = new_class(2)
>>> a.__dict__
{'multi': 4, 'str': '2'}
>>> a.__dict__.keys()
dict_keys(['multi', 'str'])

您可能还会发现pprint有帮助。

其他回答

你要这个干什么?如果不知道你的确切意图,可能很难得到最好的答案。

It is almost always better to do this manually if you want to display an instance of your class in a specific way. This will include exactly what you want and not include what you don't want, and the order will be predictable. If you are looking for a way to display the content of a class, manually format the attributes you care about and provide this as the __str__ or __repr__ method for your class. If you want to learn about what methods and such exist for an object to understand how it works, use help. help(a) will show you a formatted output about the object's class based on its docstrings. dir exists for programatically getting all the attributes of an object. (Accessing __dict__ does something I would group as the same but that I wouldn't use myself.) However, this may not include things you want and it may include things you do not want. It is unreliable and people think they want it a lot more often than they do. On a somewhat orthogonal note, there is very little support for Python 3 at the current time. If you are interested in writing real software you are going to want third-party stuff like numpy, lxml, Twisted, PIL, or any number of web frameworks that do not yet support Python 3 and do not have plans to any time too soon. The differences between 2.6 and the 3.x branch are small, but the difference in library support is huge.

attributes_list = [attribute for attribute in dir(obj) if attribute[0].islower()]

检查模块:

inspect模块提供了几个有用的函数来帮助获取 有关活动对象的信息,如模块、类、方法、 函数、回溯、帧对象和代码对象。


使用getmembers()可以看到类的所有属性及其值。要排除私有或受保护的属性,请使用. startwith('_')。要排除方法或函数,请使用inspect.ismethod()或inspect.isfunction()。

import inspect


class NewClass(object):
    def __init__(self, number):
        self.multi = int(number) * 2
        self.str = str(number)

    def func_1(self):
        pass


inst = NewClass(2)

for i in inspect.getmembers(inst):
    # Ignores anything starting with underscore 
    # (that is, private and protected attributes)
    if not i[0].startswith('_'):
        # Ignores methods
        if not inspect.ismethod(i[1]):
            print(i)

注意,ismethod()用于i的第二个元素,因为第一个元素只是一个字符串(它的名字)。

跑题:类名使用CamelCase。

如前所述,使用obj。__dict__可以处理常见情况,但有些类没有__dict__属性,而使用__slots__(主要是为了提高内存效率)。

举个更有弹性的例子:

class A(object):
    __slots__ = ('x', 'y', )
    def __init__(self, x, y):
        self.x = x
        self.y = y


class B(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y


def get_object_attrs(obj):
    try:
        return obj.__dict__
    except AttributeError:
        return {attr: getattr(obj, attr) for attr in obj.__slots__}


a = A(1,2)
b = B(1,2)
assert not hasattr(a, '__dict__')

print(get_object_attrs(a))
print(get_object_attrs(b))

这段代码的输出:

{'x': 1, 'y': 2}
{'x': 1, 'y': 2}

注一: Python是一种动态语言,它总是更好地了解你试图从中获取属性的类,因为即使这些代码也可能错过一些情况。

注2: 这段代码只输出实例变量,这意味着不提供类变量。例如:

class A(object):
    url = 'http://stackoverflow.com'
    def __init__(self, path):
        self.path = path

print(A('/questions').__dict__)

代码输出:

{'path': '/questions'}

这段代码不打印url类属性,可能会省略所需的类属性。 有时,我们可能认为属性是实例成员,但它不是,也不会在本例中显示。

>>> class new_class():
...   def __init__(self, number):
...     self.multi = int(number) * 2
...     self.str = str(number)
... 
>>> a = new_class(2)
>>> a.__dict__
{'multi': 4, 'str': '2'}
>>> a.__dict__.keys()
dict_keys(['multi', 'str'])

您可能还会发现pprint有帮助。