Variable inside module

[Alex Martelli]

Marcelo A. Camelo wrote:

> 
> Hi!
> 
> Can someone please explain-me what is
> happening here:
> 
> Given the followin bar.py file (placed
> inside a foo/ directory):
> 
> var = 'foo'
> 
> def SetVar():
> global var
> var = 'bar'
> 
> def PrintVar():
> global var
> print 'var:', var
>       
> In the same foo/ directory, I've placed
> the following __init__.py:
> 
> from bar import *

"from X import" binds names in the current module (or
current local namespace) to the values those names
hold _at this time_ in module X.  And this is all it
ever does and all it will ever do.


> Then, in the interactive python interpreter:
> 
> >>> import foo
> >>> print foo.var
> foo
> >>> foo.PrintVar()
> var: foo
> >>> foo.SetVar()
> >>> foo.PrintVar()
> var: bar
> >>> print foo.var
> foo
> >>>
>       
> What I don't understand is that foo.var seems
> to be two different variables: one accessed
> inside the bar.py file and one accessed from
> within the python interpreter. What is going on
> here?

Essentially the same thing as having, in foo/__init__.py
(which is the module body for "module foo" -- that's how
packages work):

import bar
var = bar.var
SetVar = bar.SetVar
PrintVar = bar.PrintVar
del bar

any future rebinding of bar.var will have no effect
on what foo.var is bound to now.

Yes, there ARE two different names (and variables are
just that -- names): foo.var and bar.var.


I've often recommended forgetting the existence of
statement from -- the confusion it can cause is not
justified by the modest advantages it can provide
when compared to using import (plus potentially one
or more assignments).


Alex