Python and generic programming

[Terry Reedy]

"Jive Dadson" <jdadson at yahoo.com> wrote in message 
news:419EEEAA.D3C1046F at yahoo.com...
> How about specialization?  I'm relatively new to Python.  I ask for
> information, not to be argumentative.
>
> If you have, for example, several data-types for matrices, how do you
> write code that will automatically find the right routine for quickly
> multiplying a vector by a diagonal matrix represented as a vector, and
> automatically call the right code for multiplying by a sparse matrix
> represented by some sparse coding, etc?

Specialization goes in special methods -- the ones named __xxx__ -- of 
which there are now 50-100.  For each pair of classes, at least one of the 
two must know how to do xxx on the other.  There is no way to get around 
the n square problem, but Python pushes it into individual operations so 
you only need one function that uses the operation.  So planning is 
required for a system of user-defined classed such as multiple matrix 
implementations.

For more, see the ref manual and the section on user classes.  Also check 
'special methods' in the index.

Terry J. Reedy