I would like to achieve something similar to this construction:
class Outer:
class A:
foo = 1
class B:
def __init__(self):
self.bar = A.foo
Outer.B().bar # ==> 1
But this fails with
NameError: name 'A' is not defined
I'm not even sure I understand why as A is (I thought) in scope.
Could you help me clarify why this doesn't work and how I could get around it?
Names are looked up only in globals, locals, and nonlocal cells (but you don't have a closure here).
Write Outer.A instead of A, or consider making Outer a module.
Outer is not available for code executed at class scope. It is available for code executed at function scope, since the functions are only executed later. Note also that __class__ exists, but it's mainly useful for reload or copy-pasted code to prevent typos.It works if you use Outer.A.foo.
Just like what you did for Outer.B().bar: do the same for self.bar=Outer.A().foo
Inner classes in Python do not have acces to the members of the enclosing class. A is not in scope of B as you state. A and B are both in scope of Outer, but they do not know of each other. Therefore a possible solution to your problem:
class Outer:
class A:
foo = 1
class B:
def __init__(self, class_a):
self.bar = class_a.foo
def __init__(self):
self.a = self.A()
self.b = self.B(self.a)
print(Outer.A.foo) # 1
print(Outer.B.bar) # AttributeError: type object 'B' has no attribute 'bar'
outer = Outer()
print(outer.a.foo) # 1
print(outer.b.bar) # 1
A, you would have to useOuter.A, as you'd have to inB.__init__. But why are you using nested classes to begin with? It's not a common pattern in Python... what advantage is it providing?