global variables in imported modules

[vsoler]

On 17 mayo, 00:52, Patrick Maupin <pmau... at gmail.com> wrote:
> On May 16, 5:38 pm, James Mills <prolo... at shortcircuit.net.au> wrote:
>
> > On Mon, May 17, 2010 at 8:26 AM, vsoler <vicente.so... at gmail.com> wrote:
> > > However, can I be 100% sure that,no matter how I access variable
> > > 'x' (with config.x or mod.config.x) it is always the same 'x'. I mean
> > > that either reference of 'x' points to the same id(memory position)?
>
> > Yes it does unless you re-assign it.
>
> > --James
>
> To expand a bit on what James is saying:
>
> If, for example, inside your main module, you got tired of typing
> "mod.config.x" everywhere you were using it, and decided that you
> could make a local reference to the same variable:
>
> x = mod.config.x
>
> Now, whenever you use just plain x inside the main module, you are
> also referencing the exact same object, *until* some other function
> decides to do:
>
> mod.config.x = y
>
> At this point in time, the 'x' inside main references the object that
> mod.config.x originally referenced, but mod.config.x now references a
> different object.
>
> Unlike C, for example, where the assignment operator physically places
> an item into a specific memory location (either fixed globally or
> within a stack frame), the assignment operator in python simply stores
> a key/value pair into a namespace dictionary.  So whenever you
> retrieve a value from the dictionary using that key, you will get the
> value that was last associated with that key.
>
> So, 'mod.config.x' will first retrieve the object associated with the
> key 'mod' from the main module's namespace dictionary, then will
> retrieve the object associated with the key 'config' from that
> module's namespace dictionary, then will retrieve the object
> associated with the key 'x' from that module's namespace dictionary.
> Unless you later modify any of those key/value pairs, subsequent
> retrieval will always result in the same final value.
>
> Regards,
> Pat

Really interesting, it helps a lot.

Thank you