How do python submodules share a scarce resource between them?

I am breaking up a large monolothic python file into six separate submodules.

Originally in onebigfile.py, I had

conn = MySqldb.connect()
c = conn.cursor()

and then a function would use it as so:

def getFromDB():
     c.execute(sql)

Now, I have restructured my module to

NewModule/
  __init__.py
  users.py
  accounts.py
  s开发者_高级运维ixmoreofthese.py

What I'm puzzling over is what to do with semi-scarce resources like my MySQL connection.

Is there a way to access a parent namespace, e.g. conn. and c. could be put in __init__.py ? I don't want to instantiate a whole bunch of connections to MySQL. Just dumping them there and calling them as if they're part of the global namespace doesn't work.. That is:

__init__.py:
   conn = MySqldb.connect()
   c = conn.cursor() 

> import NewModule
> NewModule.users.login('a','b')
--- login function calls the Mysql c. from the global namespace and can't find it. 

To anticipate one suggestion: it makes sense to split these files -- there's roughly 50-75k worth of python, and a group of people that need to work with the code, plus there are pretty clear conceptual groupings of functionality.

You can certainly share the connection object between python modules, and your idea to have the connection be a module-scoped variable will accomplish this nicely (with a few exceptions, Python modules are singletons, so even if they are imported multiple times from different files, they are only loaded once). You probably do not want to share a single cursor object between modules, especially if you are using a multi-threaded environment (e.g. running a web application in mod_wsgi or similar).

One suggestion might be to move the connection into a database-specific module, like db.py, and initialize/access it with a get_connection() method. This will allow your application to bootstrap and load any configuration it needs to connect (username, password, hostname) gracefully. This might be as simple as:

# db.py
connection = None
def get_connection():
    global connection
    if not connection:
        connection = MySqldb.connect() # possibly with configuration vars passed in
    return connection

Your other code which uses the databse could look like:

# other_module.py
import db
curs = db.get_connection().cursor()
# do stuff
curs.close()

What I'm puzzling over is what to do with semi-scarce resources like my MySQL connection.

I'm not sure the way I do is particularly pythonic, but I simply put my "stuff-to-be-used-by-many-modules" in a separate module that I import individually in every module I need to use it in.

EDIT: Class methods are what I use when I want to automatically initialise something only once.