python中的循环模块依赖性

Question

I have two modules, baselib.Database and baselib.Application. In baselib.Application, I have

import baselib.Database

APP = None
class BaseApplication():
    def __init__(dbClass = baselib.Database.GenericDb...):
        global APP
        this.dbClass = dbClass
        APP = this
        etc...

In baselib.Database, I have

import baselib.Application

def getDB(dbClass = baselib.Application.APP.dbClass):
    etc...

class GenericDB():
    def __init__(self, args):
    etc...

The problem is, when I import either of these modules, I get

AttributeError: 'module' object has no attribute (modulename)

The problem seems to stem from the fact that the default arguments are evaluated during the import; if I replace getDB with

def getDB(dbClass = None):
    dbClass = dbClass or baselib.Application.APP.dbClass

and do the same thing with the other default argument, everything works fine. Is this the best/most pythonic way to do this, or should I just avoid the circular dependency entirely and combine the two modules into one file? I'd really like to keep them separate because a large part of my codebase is dependent on them.

Answer 1

I think this http://effbot.org/zone/import-confusion.htm#circular-imports may answer your question. Basically, import is also a statement. We should avoid circular module dependency.