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Date: Fri, 24 Jan 2014 09:20:37 +0100
From: Johannes Schneider <johannes.schneider@galileo-press.de>
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To: python-list@python.org
Subject: Re: SIngleton from __defaults__
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Xref: csiph.com comp.lang.python:64666

thnx guys.

On 24.01.2014 01:10, Terry Reedy wrote:
>>   Johannes Schneider <johannes.schneider@galileo-press.de> Wrote in
>>   message:
>>> On 22.01.2014 20:18, Ned Batchelder wrote:
>>>> On 1/22/14 11:37 AM, Asaf Las wrote:
>>>> Chris is right here, too: modules are themselves singletons, no matter
>>>> how many times you import them, they are only executed once, and the
>>>> same module object is provided for each import.
>>>
>>> I'm not sure, if this is the whole truth.
>>>
>>> think about this example:
>>>
>>> cat bla.py
>>> a = 10
>>>
>>> cat foo.py
>>> from bla import a
>
> This makes a a global in foo, bound to 10
>
>>> def stuff():
>>>           return a
>
> This a refers to the global a in foo.
>
>>> cat bar.py
>>> from foo import stuff
>>> print stuff()
>>> a = 5
>
> This bar.a is irrelevant to the behavior of stuff.
>
>>> print stuff()
>>>
>>> from bla import *
>>> print a
>>>
>>> python bar.py
>>> 10
>
> foo.a == 10
>
>>> 10
>
> foo.a == 10
>
>>> 10
>
> bla.a == 10
>
>>> here the a is coming from bla
>
> Twice
>
> and is known in the global namespace.
>
> There is no global namespace outside of modules.
>
>>> the value differs in stuff()
>
> No it does not.
>
> and before/after the import statement.
>
> foo.a does not change. bar.a is never used.
>
>>> So the instance of the module differs
>
> Nope. Each of the three module instances is constant. The bindings
> within each could change, but there are no rebinding in the code above.
>


-- 
Johannes Schneider
Webentwicklung
johannes.schneider@galileo-press.de
Tel.: +49.228.42150.xxx

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