[Tutor] module versus file

[Kent Johnson]

Kermit Rose wrote:
> Are you saying that any .py file that I save in math\factoring
> can be imported?

Yes

>  You already have
> many modules installed as part of the standard library and any
> third-party add-ons you have installed.
>  
> **********
>  
> Yes.   I'm impressed with the listing in built_in.
>  
> I assumed system modules were handled in a different way than user modules.

Many system modules are written in Python and handled the same way as 
user modules - they are found by searching sys.path. The actual files 
are in C:\Python24\Lib

Some system modules are written in C, they are still on sys.path but the 
modules are called .pyd.

Some system modules are built-in to Python and don't correspond to an 
actual file in the file system.
>  
> *********
>  
>  
> If you are working with a module from the interpreter and you make
> changes to the module, you have to reload it with the command
>   >>> reload(factor30)
>  
> *****
>  
> I will try the reload command next time I work with factor30. 
>  
> This won't work for local names (from factor30 import xx)! Just use the
> full name to access any elements of factor30, e.G. factor30.gcd. Read
>  
> ******
>  
> In order to have the shorter name,
>  
> gcd 
>  
> instead of factor30.gcd,
>  
> I prepare by
>  
> typing 
>  
> from factor30 import gcd

If you do this, reload(factor30) will not get you a new copy of gcd 
because gcd is bound to the old function.
>  
>  
> Once someone said that modules and files are not the same thing.
>  
> This statement left me puzzled.  Why not?

Most modules do have corresponding files. The exceptions are the ones 
built-in to Python. In fact modules have a __file__ attribute that tells 
you where it came from; try typing
factor30.__file__

Kent