Use a class in the context of a different module

Question

I want to modify some classes in the standard library to use a different set of globals the ones that other classes in that module use.

Example

This exampl

Answer 1

Globals are rarely a good idea.

Implicit variables are rarely a good idea.

An implicitly-used global is easy to indict as also "rarely good".

Additionally, you don't want A.__init__() doing anything "class-level" like updating some mysterious collection that exists for the class as a whole. That's often a bad idea.

Rather than mess with implicit class-level collection, you want a Factory in module_a that (1) creates A or B instances and (b) updates an explicit collection.

You can then use this factory in module_b, except with a different collection.

This can promote testability by exposing an implicit dependency.

module_a.py

class Factory( object ):
    def __init__( self, collection ):
        self.collection= collection
    def make( self, name, *args, **kw ):
        obj= eval( name )( *args, **kw )
        self.collection.append( obj )
        return obj

module_collection = []
factory= Factory( module_collection )

module_b.py

module_collection = []
factory = module_a.Factory( module_collection )

Now a client can do this

import module_b
a = module_b.factory.make( "A" )
b = module_b.factory.make( "B" )
print( module_b.module_collection )

You can make the API a bit more fluent by making the factory "callable" (implementing __call__ instead of make.

The point is to make the collection explicit via a factory class.