Can't retrieve varname of subclass as inherited or own attribute about python-varname

[pwwang]

As @alexmojaki explained, here are some detailed solutions:

1. Use frame=2, but the class can only be subclassed once:

# with varname v0.5.6+
from varname import varname

class Item:
    def __init__(self, slots = 1):
        self.slots = slots
        self.varname = varname(frame=2)
        
class Child(Item):
    def __init__(self):
        super().__init__()
        
child = Child()
print(child.varname) # child

2. Use __init_subclass__ to increment the frame automatically:

# with varname v0.5.6+
from varname import varname

class Item:
    FRAME = 1
    
    def __init__(self, slots = 1):
        self.slots = slots
        self.varname = varname(frame=self.__class__.FRAME)
    
    def __init_subclass__(cls):
        cls.FRAME += 1
        
class Child(Item):
    def __init__(self):
        super().__init__()
        
class Grandchild(Child):
    def __init__(self):
        super().__init__()
        
child = Child()
print(child.varname) # child

grandchild = Grandchild()
print(grandchild.varname) # grandchild

3. with the ignore argument from v0.6.0, which will be coming soon:

# with varname v0.6.0 (coming soon)
from varname import varname

class Item:
    def __init__(self, slots = 1):
        self.slots = slots
        self.varname = varname(ignore=Child.__init__)
        
class Child(Item):
    def __init__(self):
        super().__init__()
        
child = Child()
print(child.varname) # child

4. or to make it general, you can wrap the subclasses in a namespace or a submodule:

# with varname v0.6.0 (coming soon)
import __main__
from varname import varname

class Item:
    def __init__(self, slots = 1):
        self.slots = slots
        self.varname = varname(ignore=(__main__, 'Namespace.*.__init__'))

class Namespace:
    class Child(Item):
        def __init__(self):
            super().__init__()
            
    class Grandchild(Child):
        def __init__(self):
            super().__init__()
        
child = Namespace.Child()
print(child.varname) # child

grandchild = Namespace.Grandchild()
print(grandchild.varname) # grandchild

[alexmojaki]

Essentially Item.__init__ looks up one frame, finds super().__init__(), and can't get a varname for that.

If people only ever construct subclasses of Item and never write foo = Item() directly, you could use varname(frame=2) to skip the Child.__init__ frame, but it wouldn't work if you also made a subclass of Child.

You could write varname(ignore=[(module_containing_Child, 'Child.__init__')]) (a more convenient API is on its way in #39) but you would need to know every subclass of Item. You could keep track of that list by implementing __init_subclass__ in Item.

Or every subclass of Item could set self.varname = varname() itself and only call super().__init__() after, while Item.__init__ could check if self.varname already exists before setting it.

It's hilarious how much work has gone into ignoring frames in the upcoming #39 and still it wouldn't help with this.

[pwwang]

@stevenzych
v0.6.0 is there. Now you can take the solutions that work with v0.6.0.

Feel free to reopen this or open a new one if you have other questions.