Python "class property" and "class function"

Question

class Test(object):
    def __init__(self):
        self.name = "changzhi"

    @property
    def __name__(self):
        return self.name

>>> a = Test()
>>> a.__name__
>>> "changzhi"
>>> a.name
>>> "changzhi"
>>> a.__name__() 
    Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    TypeError: 'str' object is not callable

Here are my thoughts:

When I run a.__name__, it returns "changzhi" because __name__ is a property of class Test(object) which is modified by "@property".
When I run a.name, it returns "changzhi" because name is a class property which is defined by __init__.
When I run a.__name__(), it occurs an error because __name__ is a class property ,not a class function Do all of my thoughts right ? Could someone explains to me ? And what the differences between __name__ and self.name(in __init__) ? Thanks a lot!

aIKid · Accepted Answer · 2014-01-17 07:06:15Z

3

Decorating a function with self.property is just a fancy way of making a property. You can also do it manually like this:

>>> class X:
    def __init__(self):
        self.name = "Me"
    def set_name(self, other):
        self.name = other
    def get_name(self):
        return self.name + "ABCDE"
    dynamicName = property(get_name, set_name)


>>> inst = X()
>>> inst.dynamicName
'MeABCDE'
>>> inst.dynamicName = "You"
>>> inst.dynamicName
'YouABCDE'

Note that dynamicName is a property, not a function. Well, it's just a syntatic sugar. Now, let's move on to your question. We can do this by using the @property decorator:

>>> class Y:
    def __init__(self):
        self.name = "Me"
    @property
    def dynamicName(self):
        #This would be the getter function
        return self.name + "ABCDE"
    @dynamicName.setter
    def set_name(self):
        self.name = other


>>> inst = Y()
>>> inst.dynamicName
'MeABCDE'

In the snippet above, dynamicName is decorated by the property function. But, result of this decoration is not a function, but an attribute! This leads to your confusion.

You can simply test it:

>>> type(inst.dynamicName)
<class 'str'>

Hope this helps!

edited Jan 17, 2014 at 7:06

answered Jan 17, 2014 at 6:54

aIKid

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2 Comments

changzhi Over a year ago

The type of inst.dynamicName is <class 'str'> because it is modified by @property. Does it right?

aIKid Over a year ago

You can learn more about decorators in this question. Actually, when you decorate a function a with @b, you're just calling b(a). The returned attribute depends on the b function.

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