Problem with static variable

Question

I'm trying to declare static variable and now my code is:

class StaticClass:
    varA = 'hello'

    @staticmethod
    def staticMethod():
        varA='bye'

Result of code below is hello. Why not 'bye' ?

StaticClass.staticMethod()

print StaticClass.varA

That looks like a Java pattern, not like Python. What are you trying to achieve? — Sven Marnach
– Sven Marnach, Commented Feb 15, 2011 at 12:24
I'm trying to declare variable in one method , and have this variable accesable from other static methods in this class , and from other other class. — user278618
– user278618, Commented Feb 15, 2011 at 12:27
@user278618: remember that this is Python, not Java, as @Daniel Roseman said. Maybe you've to re-design your classes before doing things like this. Have you considered using python properties? — Markon
– Markon, Commented Feb 15, 2011 at 13:49
"declare static variable" has no meaning in Python. Nothing is "declared". Why do you think you need this? — S.Lott
– S.Lott, Commented Feb 15, 2011 at 16:21

Sven Marnach · Accepted Answer · 2011-02-15 12:26:34Z

4

The code in staticMethod() assigns the string bye to the local variable varA, then returns, dropping the local variable. An assignment inside a function always creates local variables in Python. A staticmethod in Python has no means of accessing the class at all -- you need a classmethod for this purpose:

class StaticClass:
    var_a = 'hello'

    @classmethod
    def cls_method(cls):
        cls.var_a = 'bye'

answered Feb 15, 2011 at 12:26

Sven Marnach

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2 Comments

user278618 Over a year ago

output of StaticClass.cls_method() print StaticClass.varA is 'hello'

Sven Marnach Over a year ago

@user278618: Are you sure? Notice that I renamed varA to var_a because CamelCase is only used for class names in Python.

mdeous · Accepted Answer · 2011-02-15 12:28:07Z

1

It's because the varA you define in StaticClass.staticMethod() is in the method's namespace, not in the class namespace, if you want to access the class' varA you should do something like:

StaticClass.varA = 'bye'

By the way, you don't need to create a staticmethod to do this.

answered Feb 15, 2011 at 12:28

mdeous

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