class Outer(object):
class InnerBase(object): _var = {'foo', 'bar'}
class Derived(InnerBase):
_var = _var | {'baz'} # NameError: name '_var' is not defined
_var = InnerBase._var | {'baz'} # name 'InnerBase' is not defined
_var = Outer.InnerBase._var | {'baz'} # free variable 'Outer'
# referenced before assignment in enclosing scope
Moving _var in Outer
does not help - moving it in module scope would work but defeats the purpose of having classes. So how to go about that ?
EDIT: coming from Java so the scoping rules of classes are a head scratcher for me - a briefing would be appreciated. This works btw:
class Derived(InnerBase): pass
Derived._var = InnerBase._var | {'baz'}
but it's not the pinnacle of elegance.
Related: Nested classes' scope? - but here we specifically want to access our parent class (rather than the Outer type)
EDIT2: What I am actually after is a _var = __class__._var
-like syntax (or hack), or an explanation as to why it's not there
When you put it in a method it works.
So my impression is that it's all about initialization.
You can bypass the
class
statement and use an explicit call totype
.This works because
Derived._var
is not being set via an assignment statement in theclass
statement definingDerived
, but is imported from a dictionary you create in the same environment asInnerBase
itself.Python never searches for a name in enclosing class statements. Mark Lutz uses the acronym LEGB to summarize scope in his introduction to Python (Learning Python): Python searches the local scope, then the local scope of any enclosing
def
statements, then the global scope, and finally the built-in scope. Class statements are excluded from this scope list; Python does not search enclosing class statements for a name.One solution is to un-nest your classes. In Python, using un-nested classes is often preferred for its simplicity. But, of course, there are good reasons to nest classes as well. Why have you nested
InnerBase
? I wonder if you might have nested that class because of your experience in Java. Would the following work for you just as well?The moment you nest these two class statements under another class statement they will be excluded from name searches, since they have become part of the larger class statement and are thus excluded from the searching of the various scopes.