SimpleNamespace 和空类定义之间的区别是什么？

下面的方法似乎对任何一种方法都有效。使用 types.SimpleNamespace的优点(除了好的 repr)是什么？还是一回事？

>>> import types
>>> class Cls():
...     pass
...
>>> foo = types.SimpleNamespace() # or foo = Cls()
>>> foo.bar = 42
>>> foo.bar
42
>>> del foo.bar
>>> foo.bar
AttributeError: 'types.SimpleNamespace' object has no attribute 'bar'

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小开

最佳答案

This is explained pretty well in the types module description. It shows you that types.SimpleNamespace is roughly equivalent to this:

class SimpleNamespace:
def __init__(self, **kwargs):
self.__dict__.update(kwargs)


def __repr__(self):
keys = sorted(self.__dict__)
items = ("{}={!r}".format(k, self.__dict__[k]) for k in keys)
return "{}({})".format(type(self).__name__, ", ".join(items))


def __eq__(self, other):
return self.__dict__ == other.__dict__

This provides the following advantages over an empty class:

It allows you to initialize attributes while constructing the object: sn = SimpleNamespace(a=1, b=2)
It provides a readable repr(): eval(repr(sn)) == sn
It overrides the default comparison. Instead of comparing by id(), it compares attribute values instead.

小开

A class types.SimpleNamespace provides a mechanism to instantiate an object that can hold attributes and nothing else. It is, in effect, an empty class with a fancier __init__() and a helpful __repr__():

>>> from types import SimpleNamespace
>>> sn = SimpleNamespace(x = 1, y = 2)
>>> sn
namespace(x=1, y=2)
>>> sn.z = 'foo'
>>> del(sn.x)
>>> sn
namespace(y=2, z='foo')

from types import SimpleNamespace


sn = SimpleNamespace(x = 1, y = 2)
print(sn)


sn.z = 'foo'
del(sn.x)
print(sn)

output:

namespace(x=1, y=2)
namespace(y=2, z='foo')

This answer may also be helpful.