Python: Static class attribute of the class itself

Question

I recently made a class. Let's say that the class is declared as below.

class MyClass(object):
    def __init__(self, modifiers):
        ....

The problem is, I want to create constant instances of the class:

class MyClass(object):
    def __init__(self, modifiers):
        ....

    CONSTANT_MEMBER_1 = MyClass(my_modifiers)
    CONSTANT_MEMBER_2 = MyClass(my_modifiers)

Unfortunately, Python won't allow me to do so, with error:

E    NameError: global name 'MyClass' is not defined

Any solution for this problem?

One alternative would be creating a 'static' method for the class that will return a same object each time it's called (e.g., MyClass.CONSTANT_MEMBER_1()). But I think I would still prefer to access it using MyClass.CONSTANT_MEMBER_1.

Thanks.

Can you explain the use case a little more? A "static attribute or method" has a specific meaning here, but you seem to be using "static member" to refer to: "an instance of the class that never changes" — brianpck
– brianpck, Commented Oct 25, 2016 at 15:53
@brianpck yes, I meant to refer to "constant instances of the class". Edited. Thanks. — sokokaleb
– sokokaleb, Commented Oct 25, 2016 at 16:05

khelwood · Accepted Answer · 2016-10-25 15:57:17Z

2

You can assign to class variables right after the class has been defined.

class MyClass(object):
    def __init__(self, modifiers):
        ....

MyClass.CONSTANT_MEMBER_1 = MyClass(my_modifiers)
MyClass.CONSTANT_MEMBER_2 = MyClass(my_modifiers)

answered Oct 25, 2016 at 15:57

khelwood

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wwii · Accepted Answer · 2016-10-25 16:19:08Z

-1

Maybe make use of inheritance and custom descriptors, Python Descriptors Demystified

class MyClass(object):
    def __init__(self, color):
        self.color = color
    def __repr__(self):
        return 'I am {}'.format(self.color)

class Foo(MyClass):
    ConstantMember_blue = MyClass('blue')
    ConstantMember_red = MyClass('red')

f = Foo('green')

>>> f
I am green
>>> f.ConstantMember_blue
I am blue
>>> f.ConstantMember_red
I am red
>>> Foo.ConstantMember_blue
I am blue
>>> Foo.ConstantMember_red
I am red
>>>

answered Oct 25, 2016 at 16:19

wwii

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