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Tkinter bug ?

Fredrik Lundh fredrik at pythonware.com
Mon Jul 26 13:28:13 EDT 1999 
Stephane Conversy <conversy at lri.fr> wrote:
> ok, but does it have something to do with the fact that in one case
> I do a from file1 import * and in the other import file1 ?

now that you mention it...

forget my previous answer (for the moment; you
might stumble upon that problem later).

...

if you'd added some "print photo" statements to File2.py
in your first example, you would have noticed that the
variable is None both before and after the call to
create_photo().  if you'd added similar statements to
File1.py, you would have noticed that create_photo
actually did set it to something else.

the reason for this is that all variables in Python contain 
references to objects, not the objects themselves.  the
assignment statement just changes a variable to refer to
a new value, it doesn't copy the object itself (nor does
this modify the old value).

and import is just a fancy assignment statement; the
from-import form copies object references from the
imported module, not the objects itself.

in other words, after the import, there are TWO "photo"
variables, one in each module.  and changing one to refer
to a new object doesn't automatically change the other
one.

> I'm a beginner in Python, and don't know exaclty how modules
> are implemented...

but in that case, you shouldn't be using from-import at all !

for more details, see:
http://www.pythonware.com/people/fredrik/fyi/fyi06.htm

note the fourth item under "Which Way Should I Use?" ;-)

</F>
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