Python and generic programming

Jive someone at microsoft.com
Sun Nov 21 01:40:56 CET 2004


I hate to break it to you Terry, but Issac did understand the question.  The
example he gave was perhaps a little fanciful, but it was on the money.
That is exactly the kind of thing I was asking about.

More typical examples of specialization may be found in the Standard
Template Library, and in the Boost Graph Library.

When you define a function in Python, you are (in effect) defining many
functions, just as Issac says.  What the byte codes eventually do depends on
type information that is acted on at runtime.  C++ has a mechanism
(templates) for acting on the type information similarly, but at compile
time.  However, a modern C++ compiler can do something beyond that.  It can
recognize special cases (which the programmer must code for) and use a
different functional form (template) for the special case than for the
generic case.  Both STL and BGL use the mechanism extensively.

jdadson at yahoo dott com

"Terry Reedy" <tjreedy at udel.edu> wrote in message
news:mailman.6647.1100967514.5135.python-list at python.org...
>
> "Isaac To" <iketo2 at netscape.net> wrote in message
> news:87actcrhlo.fsf at sinken.local.csis.hku.hk...
>
> > "Terry" == Terry Reedy <tjreedy at udel.edu> writes:
> >>    Terry> Specialization goes in special methods -- the ones named
> >>    Terry> __xxx__ -- of which there are now 50-100.
>
> > No, you don't quite understand what the OP is asking for.
>
> No, YOU are the one who does not understand, because you apparently did
not
> do me the courtesy of reading my entire post, in which I quoted the
> question I answered.  Here again is the OP's question about *type*
> specialization *in Python*:
>
> >>> 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?
>
> The has NOTHING to do with writing base cases in recursive C++ template
> metaprogramming (which, ironically, uses the compiler as an interpreter).
>
> Although there may be other answers now and in the future, the answer I
> gave is the straightforward standard answer for Python today.
>
> Terry J. Reedy
>
>
>





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