Question

Three module exists. Cfg, Main and Component

Cfg.py

value = 0

Component.py

import Cfg

class index:
    def GET(self):
        return Cfg.value

Main.py

from Test import Cfg
import Component

urls = ('/', 'Component.index')

if __name__ == '__main__':

    Cfg.value = 1
    app = web.application(urls, globals())
    app.run()

Get method of Component.Index returns 0, but i’m expecting 1. What did i miss?

Edit #1

first modification main.py to test :

from test import Cfg
import Component
import test

if __name__ == '__main__':
    importedCfg = id(Cfg)
    cfgInComponent = id(Component.Cfg)
    cfgInTest = id(test.Cfg)

    print importedCfg, cfgInComponent, cfgInTest
    print importedCfg == cfgInComponent == cfgInTest

Result :

36202928 36203088 36202928
False

Second modification in main.py :

import Cfg
import Component

if __name__ == '__main__':
    importedCfg = id(Cfg)
    cfgInComponent = id(Component.Cfg)
    # cfgInTest = id(test.Cfg)

    print importedCfg, cfgInComponent
    print importedCfg == cfgInComponent 

36858160 36858160 True

if you do not want to create multiple instance you should follow the second way.

Answer 1

Compare the result of:

from Test import Cfg
import Component

if __name__ == '__main__':
    assert id(Cfg) == id(Component.Cfg)

and

import Cfg
import Component

if __name__ == '__main__':
    assert id(Cfg) == id(Component.Cfg)

this means that doing a “from module” import creates different instances of Cfg. (I wasn’t aware of this either).

This behavior is present in Python 2.7 and Python 3.2 (Python 2.6 wasn’t tested).