Good practice sharing resources between modules?

Question

I am reorganizing my code and therefore creating new namespaces. I'm changing "static" classes (classes with @staticmethod in each method) for modules. This is the way to go, right?

The problem is that I have doubts on how to share the resources between these modules.

Let's say I had a module from which I was doing all connections to database, and of course all classes/methods were sharing the variable which stored the DB cursor (I'm using SQLite). Now, in different modules, they also have to share the cursor.

So, my ideas:

• Declare the global variable in each module. But globals are evil, eat children and steal our jobs. So I don't know if this is the way to go.

  '''Sub Module 1'''
  
  global database_cursor
  

• Import the "father" database_module with the original database_cursor and use something like this:

  '''Sub Module 1'''
  
  db_cursor = database_module.database_cursor
  

This second looks fine in this case, but I think in many cases will lead to recursive imports, which I guess it´s something to avoid.

Answer 1

Your second method is the way to go. Python imports are singleton by nature. When a module is imported multiple times it is only executed the first time. Subsequent imports fetch the module object instance from the globals. More on that here.

shared.py:

class Shared:
    def __init__(self):
        print("Init shared")

    def do_stuff(self, from_mod):
        print("Do stuff from {0}. I am instance {1}".format(from_mod, self))

shared = Shared()

foo.py

import shared

shared.shared.do_stuff("foo")

bar.py

import foo
import shared

shared.shared.do_stuff("bar")

If we execute bar.py we get:

>>> Init shared
>>> Do stuff from foo. I am instance <shared.Shared instance at 0x10046df38>
>>> Do stuff from bar. I am instance <shared.Shared instance at 0x10046df38>

So in your case you can reference database_module from anywhere you want and it gets initialized only once, therefore effectively sharing your connection.