doc: override by derived container class

I would like a derived container class to be able to provide a dependency for a base container. It would seem that this isn’t possible now:

class Base(containers.DeclarativeContainer):
  to_override = providers.Dependency(instance_of=str)

# method 1 -- override attribute
class Derived1(Base):

    other_dependency = providers.Dependency(instance_of=Foo)
    to_override = other_dependency.provided.some_string_attr

# method 2 -- use constructor
class Derived2(Base):

    def __init__(self, other_dependency: Foo, **kw):
        super_kw = kw.copy()
        if 'to_override' not in super_kw:
            super_kw['to_override'] = other_dependency.some_string_attr
        super().__init__(other_dependency=other_dependency, **super_kw)

    other_dependency = providers.Dependency(instance_of=Foo)

In either case I get dependency_injector.errors.Error: Dependency is not defined when I build a derived object and attempt to access to_override.

[rmk135]

Added docs for the @containers.copy() decorator: https://python-dependency-injector.ets-labs.org/containers/copying.html. Closing the issue.

PS: @shaunc , appreciate your review if you would have some time. Please, drop me a line if there are any improvements on your mind.

[rmk135]

Hey @shaunc . I’m away from computer right now, will take a look soon.