Hygenic Macros

Adriaan Renting renting at astron.nl
Tue Oct 18 14:17:43 CEST 2005


Using numarray/pylab there's also dot:
>>> from pylab import *
>>> A = array(range(10))
>>> B = array(range(10))
>>> A * B
[ 0, 1, 4, 9,16,25,36,49,64,81,]
>>> dot(A, B)
285

It might also make your code more readable. I would like "A dot B", but even using ipython
I can only get as close as "dot A, B"
 
>>>Dan Farina <nntp.20.drfarina at recursor.net> 10/18/05 1:33 pm >>> 
David Pokorny wrote: 
>Hi, 
> 
>Just wondering if anyone has considered macros for Python. I have one 
>good use case. In "R", the statistical programming language, you can 
>multiply matrices with A %*% B (A*B corresponds to pointwise 
>multiplication). In Python, I have to type 
> 
>import Numeric 
>matrixmultiply(A,B) 
> 
>which makes my code almost unreadable. 
> 
>Thanks, 
>David 
 
The problem here is that Python's parse trees are of non-trivial ugliness. 
 
A page on the compiler.ast module: 
http://docs.python.org/lib/node792.html 
 
it is, in fact, perfectly possible to write yourself a pre-processor for 
your particular application.  You may have to fiddle with the token you 
want for notation depending on how the AST fleshes out (% is used by at 
least a couple of things, after all).  My cursory familiarity with 
python grammar suggests to me that this particular choice of token could 
be a problem. 
 
I would say try it and see.  Keep in mind though that since Python's AST 
is not a trivial matter like it is in Lisp and the like that doing 
metaprogramming of this sort probably falls into the category of black 
magic unless it turns out to be very trivial. 
 
Another option is to define your own tiny class that will override the 
__mult__ method so that you can simply do: 
 
A * B 
 
Which may not be what you want. 
 
df 
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