Let’s say that I have created a bunch of Sage code — Sage functions etc. — that I wish to reuse by importing into various Sage scripts. In straight Python, one would put these functions into their own separate file and import them using the usual ` from foo import funcname as localfuncname`

type procedure. It is unclear to me what the proper procedure for doing the same in Sage is — one can’t use the same syntax for a `.sage`

file, and for example `attach('functions.sage')`

and only works in interactive Sage and stomps local variables.

However after some Googling and experimentation, I have found one method that behaves in the way that I need: namely that local variables aren’t stomped, and Sage-style syntax, like expressing a rational as a fraction, is preserved. I don’t know if this is the best way to do it, but it seems to be working, so I thought I’d share it.

First write `functions.sage`

as though it were a module file.

def myfunc(y):
var('n, x')
z1 = y
z2 = 1/2
return z1, z2

Then for the script where we want to use it (`myscript.sage`

), we preparse the Sage functions file into a Python file and copy it to a name that can be handled before importing it.

import os
os.system('sage --preparse functions.sage')
os.system('mv functions.sage.py functions.py')
from functions import myfunc
x = 2
y = 3
z1,z2 = myfunc(y)
print(x)
print(z2)

When run, `myscript.sage`

produces the following.

From the command-line

$ sage myscript.sage
2
1/2

From an interactive session:

sage: attach('myscript.sage')
2
1/2
sage: type(z2)
<type 'sage.rings.rational.Rational'>

The script produces `functions.py`

, which looks like this:

# This file was *autogenerated* from the file functions.sage
from sage.all_cmdline import * # import sage library
_sage_const_2 = Integer(2); _sage_const_1 = Integer(1)
def myfunc(y):
var('n, x')
z1 = y
z2 = _sage_const_1 /_sage_const_2
return z1, z2

It has been working out for me so far, but it seems a strange way to go about things. I’d welcome any commenters who know of a nicer way.

—

Refs: Ask Sagemath.org

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