Most Pythonic way to provide global configuration variables in config.py?

Question

In my endless quest in over-complicating simple stuff, I am researching the most 'Pythonic' way to provide global configuration variables inside the typical 'config.py' found in Python egg packages.

The traditional way (aah, good ol' #define!) is as follows:

MYSQL_PORT = 3306
MYSQL_DATABASE = 'mydb'
MYSQL_DATABASE_TABLES = ['tb_users', 'tb_groups']

Therefore global variables are imported in one of the following ways:

from config import *
dbname = MYSQL_DATABASE
for table in MYSQL_DATABASE_TABLES:
    print table

or:

import config
dbname = config.MYSQL_DATABASE
assert(isinstance(config.MYSQL_PORT, int))

It makes sense, but sometimes can be a little messy, especially when you're trying to remember the names of certain variables. Besides, providing a 'configuration' object, with variables as attributes, might be more flexible. So, taking a lead from bpython config.py file, I came up with:

class Struct(object):

    def __init__(self, *args):
        self.__header__ = str(args[0]) if args else None

    def __repr__(self):
        if self.__header__ is None:
             return super(Struct, self).__repr__()
        return self.__header__

    def next(self):
        """ Fake iteration functionality.
        """
        raise StopIteration

    def __iter__(self):
        """ Fake iteration functionality.
        We skip magic attribues and Structs, and return the rest.
        """
        ks = self.__dict__.keys()
        for k in ks:
            if not k.startswith('__') and not isinstance(k, Struct):
                yield getattr(self, k)

    def __len__(self):
        """ Don't count magic attributes or Structs.
        """
        ks = self.__dict__.keys()
        return len([k for k in ks if not k.startswith('__')\
                    and not isinstance(k, Struct)])

and a 'config.py' that imports the class and reads as follows:

from _config import Struct as Section

mysql = Section("MySQL specific configuration")
mysql.user = 'root'
mysql.pass = 'secret'
mysql.host = 'localhost'
mysql.port = 3306
mysql.database = 'mydb'

mysql.tables = Section("Tables for 'mydb'")
mysql.tables.users = 'tb_users'
mysql.tables.groups =  'tb_groups'

and is used in this way:

from sqlalchemy import MetaData, Table
import config as CONFIG

assert(isinstance(CONFIG.mysql.port, int))

mdata = MetaData(
    "mysql://%s:%s@%s:%d/%s" % (
         CONFIG.mysql.user,
         CONFIG.mysql.pass,
         CONFIG.mysql.host,
         CONFIG.mysql.port,
         CONFIG.mysql.database,
     )
)

tables = []
for name in CONFIG.mysql.tables:
    tables.append(Table(name, mdata, autoload=True))

Which seems a more readable, expressive and flexible way of storing and fetching global variables inside a package.

Lamest idea ever? What is the best practice for coping with these situations? What is your way of storing and fetching global names and variables inside your package?

Answer 1

How about just using the built-in types like this:

config = {
    "mysql": {
        "user": "root",
        "pass": "secret",
        "tables": {
            "users": "tb_users"
        }
        # etc
    }
}

You'd access the values as follows:

config["mysql"]["tables"]["users"]

---

If you are willing to sacrifice the potential to compute expressions inside your config tree, you could use YAML and end up with a more readable config file like this:

mysql:
  - user: root
  - pass: secret
  - tables:
    - users: tb_users

and use a library like PyYAML to conventiently parse and access the config file