Question

我想映射一个属性，所以我尝试了

map(lambda o: cls.prop(o), list_of_objects)

该属性在外部库中定义为：

@property
def prop(self):

但是，我收到TypeError错误。

我对它进行了测试＆＃34;未映射＆＃34;，cls.prop(an_object)工作得很好，应该是等同于an_object.prop。

我做错了什么？我怎么能做到这一点？

（我知道列表理解[o.prop for o in list_of_objects]，但我想学习并理解上面出了什么问题。）

Answer 1

A property, accessed on the class, returns the property object itself, and not the wrapped function. A property wraps three functions, the getter, setter and deleter (each of these can be None):

>>> class Foo(object):
...     @property
...     def prop(self):
...         return 'bar'
...
>>> Foo.prop
<property object at 0x107102bd8>
>>> Foo.prop.fget, Foo.prop.fset, Foo.prop.fdel
(<function Foo.prop at 0x1073366a8>, None, None)

You need to access the fget attribute to get just the getter:

map(lambda o: cls.prop.fget(o), list_of_objects)

However, this is overkill, just access the attribute directly:

map(lambda o: o.prop, list_of_objects)

or use a operator.attrgetter() object:

from operator import attrgetter

map(attrgetter('prop'), list_of_objects)

The latter has the advantage that the map() C loop won't have to step back into the Python interpreter loop to execute the lambda bytecode, attrgetter() can do it's job entirely in C making the combination faster.

在python

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