On Tue, Aug 14, 2012 at 2:24 PM, Mazhar Hussain <yam.m...@gmail.com> wrote:
>
> #mod1.py
> from mod2 import test
> test('mod1.py')
>
> #mod2.py
> def countLines(name):
> print len(open(name).readlines())
>
> def countChars(name):
> print len(open(name).read())
>
> def test(name):
> print 'loading...'
> countLines(name)
> countChars(name)
> print '-'*10
>
> Here when I imported and ran the 'test' function, it ran successfully
> although I didn't even import countChars or countLines, and the 'from'
> statement had already deleted the mod2 module object.
>
> SO I basically need to know why does this code work although
> considering the problems I mentioned it shouldn't.
mod1 gets a reference to mod2.test, but the mod2 object isn't garbage
collected. A reference exists in sys.modules. After the import, add
the following:
import sys
print sys.modules['mod2']
Also test() can access countChars() and countLines() because it was
defined in the mod2 namespace. In other words, test.__globals__ is
mod2.__globals__. An example:
#mod1.py
import mod2
mod2.test_global()
print mod2.g
#mod2.py
def test_global():
global g
g = "I'm in mod2."
#run python mod1.py
Even though test_global is called from mod1, g is created in mod2.
More namespace trivia...
When you run a module as the main script, its name is '__main__' and
other modules can "import __main__". But if you import it by the
filename, you get a new module instance with a separate namespace:
#mod1
if __name__ == '__main__':
import mod2
mod2.imp_main() #create g in __main__ and also in mod1
print g #__main__
import mod1 #self import, but mod1 instance, not __main__
print mod1.g #mod1
#mod2
def imp_main():
import __main__
import mod1
__main__.g = "__main__"
mod1.g = "mod1"
#run python mod1.py
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