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About Cython and the main Sage commands

asked 2013-07-02 01:16:52 -0500

I read the "How to import some commands?" and "Importing sage functions into cython?" topics, so I know how importing new commands in Sage and also under %cython.

I found that main commands like "factor" or "identity_matrix" which are automatically available in Sage are not under %cython. Then, it's necessary to add the lines:

"from sage.rings.arith import factor"
"from sage.matrix.constructor import identity_matrix"

Questions:

  • Why the main commands are not automatically available under %cython ?
  • Is there a line importing directly all the main commands under %cython ?
  • Or, is it a good idea to improve the Sage software so that it works directly ?

I read also that such imported commands are not "cythonised" (and so not 100 times faster).

  • Are there cythonised equivalents of all the main commands ?
  • If not, is there a project to cythonised all the main commands ?
  • Why Sage does not use directly Cython ?
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answered 2013-07-02 02:59:26 -0500

ppurka gravatar image

updated 2013-07-02 03:01:44 -0500

Just add

from sage.all import *

at the beginning of the file, or immediately after %cython.

Quite a lot of the code in sage is implemented in cython. Just have a look at the source code.

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Ok, thank you ! Does this line import all the libraries or just the main functions ?

Sébastien Palcoux gravatar imageSébastien Palcoux ( 2013-07-02 03:51:40 -0500 )edit
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This imports the same functions normally imported into Sage. That is a lot, of course. But this essentially creates a separate ".pyx" file, which (like any non-Sage file) doesn't have things automatically imported.

kcrisman gravatar imagekcrisman ( 2013-07-02 04:14:58 -0500 )edit
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answered 2013-07-02 03:28:12 -0500

Volker Braun gravatar image

If your code spends most of its time in external libraries (that are already C/Cython) then it won't benefit from being rewritten. As a general strategy I'd recommend to first write a Python prototype, then identify speed-critical parts, and then selectively rewrite these bits in C/Cython.

Cython can and will call back into Python code, in particular you can import any Python module.

The %cython magic probably should automatically import sage.all

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Thank you for your answer. I don't understand a point: it's %cython which is a magic function, there is not another function called "%cython magic" ? Becasue about %cython, I do the test and the functions "factor" and "identity_matrix" are not automatically imported.

Sébastien Palcoux gravatar imageSébastien Palcoux ( 2013-07-02 03:55:47 -0500 )edit

It's not a magic function in the same sense. It says, "this is a cell that contains Cython code to be compiled".

kcrisman gravatar imagekcrisman ( 2013-07-02 04:14:12 -0500 )edit

Ok thanks. Do you confirm that %cython does not import automatically sage.all ?

Sébastien Palcoux gravatar imageSébastien Palcoux ( 2013-07-02 04:48:26 -0500 )edit

Volker seems to imply it doesn't.

kcrisman gravatar imagekcrisman ( 2013-07-02 05:13:49 -0500 )edit

I didn't understand its sentence. So he says it doesn't but he thinks it should. So let's do it.

Sébastien Palcoux gravatar imageSébastien Palcoux ( 2013-07-02 05:41:50 -0500 )edit

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Asked: 2013-07-02 01:16:52 -0500

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Last updated: Jul 02 '13