Initializing a static field in a Python class

Question

I want to initialize a static field on declaration.

class Test:

    def _init_foo(): return 3

    foo = { _init_foo() for i in range(10)}

However, the interpreter is complaining

NameError: name '_init_foo' is not defined

How do I fix this?

Answer 1

Why this fails is explained here.

You could work around the problem by defining foo via a class decorator. This works because by the time add_foo is called, the class has been defined and _init_foo in then accessible as cls._init_foo:

def add_foo(cls):
    cls.foo = { cls._init_foo() for i in range(10) }
    return cls

@add_foo
class Test:

    def _init_foo(): return 3


print(Test.foo)
# {3}