python static variable in instance method

Question

Here is my code not working

class MyClass:
    special_items = {}
    def preload_items(self):
        special_items['id'] = "properties"

NameError: global name 'special_items' is not defined

works

class MyClass:
    special_items = {}
    def preload_items(self):
        MyClass.special_items['id'] = "properties"

Isn't it special_items a static member I can access anywhere in this class?

shx2 · Accepted Answer · 2013-03-13 18:49:00Z

2

There is no such thing as static members in python. What you defined is a class-member. The member is stored on the class object, and as you already showed, it is accessed as MyClass.special_items.

It seems that what you're trying to do is to initialize special_items. For that, classmethod is more appropriate (there's no use for self):

@classmethod
def preload_items(cls):
        cls.special_items['id'] = "properties"

Note that you can also access it as self.special_items, but it is still stored on the class object, i.e. all objects of the class access the same value.

edited Mar 13, 2013 at 18:49

answered Mar 13, 2013 at 18:38

shx2

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8 Comments

mgilson Over a year ago

Maybe suggest a classmethod for this one ... (or note that self.special_items['id'] will also work out for this simple example)

wwli Over a year ago

So I have to attach something before this special_items? No a clean way to call this variable in python?

shx2 Over a year ago

Why do you consider it not clean? You can define a global variable, but if the variable is logically-associated with MyClass, class member is way better.

mechanical_meat Over a year ago

@wwli: Perhaps it would be helpful to specify the language in which a "clean way" is used, and explain what specifically about that "clean way" you prefer over Python's semantics.

wwli Over a year ago

@bernie from c++ and java apparently you can access such a static/class variable with nothing attached :)

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