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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  
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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.
Well, dot(A, B) is better. But if you must: http://aspn.activestate.com/ASPN/Coo.../Recipe/384122

Robert Kern rk***@ucsd.edu
"In the fields of hell where the grass grows high
Are the graves of dreams allowed to die."
 Richard Harter  
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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 nontrivial 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 preprocessor 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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On Mon, 17 Oct 2005 22:23:43 0700, 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.
Yes, I see what you mean, it is pretty confusing. It almost looks like
a function that multiplies two matrices and returns the result.
Have you tried coming up with better names for your arguments than A and
B? Many people find that using selfdocumenting variable names helps make
code easier to understand.

Steven.  
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Steven D'Aprano wrote: On Mon, 17 Oct 2005 22:23:43 0700, 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.
Yes, I see what you mean, it is pretty confusing. It almost looks like a function that multiplies two matrices and returns the result.
Have you tried coming up with better names for your arguments than A and B? Many people find that using selfdocumenting variable names helps make code easier to understand.
Well, to be fair, his example was trivial. When you have more
complicated matrix expressions with transposes and conjugations and more
matrixmultiplies than you can shake a stick at, it gets ugly pretty fast.
F = dot(dot(Z, F),transpose(conjugate(Z)))
versus
from scipy import *
F = mat(F)
Z = mat(Z)
F = Z*F*Z.H

Robert Kern rk***@ucsd.edu
"In the fields of hell where the grass grows high
Are the graves of dreams allowed to die."
 Richard Harter  
P: n/a

On Tue, 18 Oct 2005 13:42:21 0700, Robert Kern wrote: Steven D'Aprano wrote: On Mon, 17 Oct 2005 22:23:43 0700, 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. Yes, I see what you mean, it is pretty confusing. It almost looks like a function that multiplies two matrices and returns the result.
Have you tried coming up with better names for your arguments than A and B? Many people find that using selfdocumenting variable names helps make code easier to understand.
Well, to be fair, his example was trivial. When you have more complicated matrix expressions with transposes and conjugations and more matrixmultiplies than you can shake a stick at, it gets ugly pretty fast.
F = dot(dot(Z, F),transpose(conjugate(Z)))
No uglier than y = sin(poly(sqrt(x)))
And of course it is allowed to do this:
F = dot(Z, F)
Z = transpose(conjugate(Z))
F = dot(F, Z)
Not everything has to be a oneliner, not even in mathematics.
versus
from scipy import * F = mat(F) Z = mat(Z) F = Z*F*Z.H
It's a matter of taste. But calling it "almost unreadable" is an
exaggeration.

Steven.  
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Hi,
Thanks  this cookbook entry is very cool!
I am somewhat worried about function call overhead from the infix hack
though... on second consideration, the infix issue is not as important
as eventually boosting the speed of the inner loop to which
matrixmultiply() belongs. For those who are interested in things like
fast math, I found http://www.scipy.org/documentation/w...rformance.html
very eyeopening. For many of the examples cited there, it is possible
to simply treat the source as a string and then do the necessary macro
transformations before passing it off to a compiler...
David
Robert Kern wrote: 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.
Well, dot(A, B) is better. But if you must:
http://aspn.activestate.com/ASPN/Coo.../Recipe/384122   This discussion thread is closed Replies have been disabled for this discussion.   Question stats  viewed: 1384
 replies: 6
 date asked: Oct 18 '05
