On 4/16/07, Gary Bunting <[EMAIL PROTECTED]> wrote:
>
> I have been trying to use some of my python code in sage but
> have been having problems, apparently because sage implements
> generic arithmetic differently to python.
SAGE implements its own integer class, which is better than
Python's in various ways. However, it has somewhat different
behavior. Your options (4 is the best but most complicated):
(1) Use Python integers instead of SAGE integers, at least
in an example like below. To make a Python integer literal,
just put r after it:
sage: x = MyList([1,2,3])
sage: 10r*x
[should work]
Alternatively, make the Python integer using int(10), though
that would be slower.
(2) It's possible we'll be able to come up with an extension to
how SAGE arithmetic works so thaty your example below works,
but you would have to wait a while.
(3) Use the SAGE libraries directly from Python. E.g.,
[EMAIL PROTECTED]:~$ sage -python
Python 2.5 (r25:51908, Feb 16 2007, 11:50:26)
[GCC 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from sage.all import *
>>> 2/3
0
>>> euler_phi(50)
20
(4) Make your class genuinely fit into the SAGE arithmetic
architecture. SAGE has a very sophisticated and thought
through "arithmetic architecture", which is much different
than Python's very naive (in the context of serious math)
approach. See the programming guide for more details.
The basic idea is that every element has a parent (container
ring of module) and there are canonical coercion rules.
Anyway, your example would be written this way (note that
you can't inherit from both ModuleElement and list):
{{{
from sage.structure.parent_base import ParentWithBase
class AllLists_class(ParentWithBase):
def __init__(self):
ParentWithBase.__init__(self, ZZ)
AllLists = AllLists_class()
class MyList(ModuleElement):
def __init__(self, v):
ModuleElement.__init__(self, AllLists)
self._list = list(v)
def _rmul_(self, other):
return MyList([other*x for x in self._list])
def _repr_(self):
return repr(self._list)
}}}
{{{
v = MyList([1,2,3])
}}}
{{{
2*v
///
[2, 4, 6]
}}}
>
> Here is a simple example:
>
> class MyList(list):
>
> def __rmul__(self, other):
> return MyList([other*x for x in self])
>
> Python:
> >>> x = MyList([1,2,3])
> >>> 10*x
> [10, 20, 30]
>
> Sage:
>
> sage: x = MyList([1,2,3])
> sage: 10*x
> ---------------------------------------------------------------------------
> <type 'exceptions.TypeError'> Traceback (most recent call
> last)
>
> /home/gbunting/algebra/comp/python/sage/<ipython console> in
> <module>()
>
> /home/gbunting/algebra/comp/python/sage/element.pyx in
> element.RingElement.__mul__()
>
> /home/gbunting/algebra/comp/python/sage/element.pyx in
> element.bin_op_c()
>
> <type 'exceptions.TypeError'>: unsupported operand parent(s) for '*':
> 'Integer Ring' and '<class '__main__.MyList'>'
>
>
> I have python code for that I use for experimenting with polynomials
> and
> differential operators and would like to use it from sage.
>
> Cheers,
> Gary
>
>
> >
>
--
William Stein
Associate Professor of Mathematics
University of Washington
http://www.williamstein.org
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