[Tutor] definition of a library

[alan.gauld@bt.com]

> On Tuesday, March 19, 2002, at 11:46  PM, dman wrote:
> > In python, libraries can be written in Python, C, or C++ 
> (and possibly some other language, but I haven't seen them).  

FWIW
I usually distinguish between modules and libraries (despite 
the definition that was quited earlier!) Libraries can be an 
amalgam of several modules. A module is a unit of reusable code.
A library is a physical file that contains reusable or shared 
code, and that may include multiple modules. Its a subtle but 
sometimes important distinction (and one not recognised 
by UML for those who care :-).

> Since I'm not quite ready to learn C or C++ (maybe tomorrow :), I can 
> just assume that if a C or C++ library is intended to be 
> embedded within Python programs, then it has already been 
> compiled appropriately?  

Yes, usually. Occasionally you may get a library in source form 
in which case you need to comile it. In most cases you just use it.

> > them via $PYTHONPATH and sys.path.  The C function dlopen() allows a
> > (C) program to link and load a .so at runtime.  Thus the interpreter
> 
> Let me stop you for a minute for a clarification -- does this 
> mean that any C programs need to be called with dlopen()?  

Yes but its the python interpreter code that does it not yours.
When you import a module thats a C module the interpreter loads 
it via this function(I assume - I haven't looked!)

> Has this been specially written so as not to require the dlopen() 
> function, or is it because it's not a .so file?

It does exist in a .so somewhere I think but it *does* need 
dlopen() its just handled by Python when you import cpickle.

The good news is that regardless of whether a module is 
implemented in Python or in C you just import it and Python 
does the rest(provided you've installed it in the right 
place and told Python where to find it of course!)

HTH

Alan G.