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?
2 Answers
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}
Comments
Before finding the class decorator option, I was initialising fields after the class declaration. I don't know which one I like less... :) I miss a static init block like in Java.
class Box:
def __init__(self, x):
self.x = x
Box.count += 1 # static field usage
@staticmethod
def instance_count():
return Box.count # static field usage
Box.count = 0 # static field initialisation
b1 = Box(10)
b2 = Box(20)
print(Box.count) # 2
footo be same and shared for all instances, just writefoo = 3. But it will not be static anyway.