Modules, namespaces, parents, and import

[Dietrich Epp]

On Feb 3, 2004, at 10:28 PM, Dan Williams wrote:

> Hi people
>
> I've just joined the Python list and although I'm sure my question 
> must be
> asked fairly frequently, I have been unable to find an answer after 
> two days
> of searching. For the record, my total Python experience is also two 
> days :)
> (I come from a C++ background though, so I have good programming 
> knowledge
> in general).
>
> My question is thus: how do I reference a parent module and its 
> children?

--- foo/__init__.py ---

import module1
a = 5
module1.DoStuff

--- foo/module1.py ---

import sys
import foo

def DoStuff():
     print foo.a
     sys.exit(0)

------

The idea is that when you look at a single source file, all the imports 
are right there.  Each module has its own namespace, and doesn't 
inherit from its parent.  Otherwise it would get cluttered to heck!

You said that importing sys from module1 is inefficient and 
impractical.  Why?  It takes more writing to use parent.sys.bar instead 
of just sys.bar... I'd regard putting 'parent' in front of every 
occurrence of 'sys' impractical.  Plus, if you use parent.sys, it looks 
like your using the module 'sys' from the package 'parent', which isn't 
the case.

You might have been thinking about speed... but don't.  First of all, 
you're forgetting the first rule of optimization: Don't.  Second rule 
of optimization: Don't, yet.  Third rule of optimization: The 
bottleneck isn't where you think it is.  For a lot of code, the 
bottleneck is actually writing the code.  So to make the whole process 
faster, write the code faster.  This means write less code, and 
especially don't do anything just because you think it would be faster 
for the computer.  Often you're wrong, and you've just wasted a lot of 
your time, and the computer is probably fast enough.

And finally, using 'parent.sys.exit' is slower because Python has to 
get the value of 'parent', then get its attribute named 'sys', then get 
sys's attribute named 'exit', than call it.  If you import sys 
directly, you don't have to retrieve it from 'parent' every time, and 
no, this does not load additional code -- it just references the 
already loaded module.

Please, please don't be seduced by optimization.  Make your code work.  
It is far easier to optimize correct code than correct optimized code.  
Also, never optimize code not checked into a revision control system.