[Solved] Difference about divide operator in python2 and sage

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I am writing a package (I want to use "import" to import it into sage).

I found that in the package (say, test.py), if I write

from sage.all import *

def test():
    var('a')
    print -1/2, -a/2, (-1/2)*a

and in sage type

import test; test.test()

I got "-1 -1/2*a -a"

This is different from directly run the above commands from sage.

I know in python 2, -1/2 returns -1. But is there a way to write "minus one half" (-1/2) in a package, say, test.py?

I know I could use load or attach to load a .sage package. However, they don't have namespace and I hope to have namespace as in python.

I could also use 1/2.0, which returns 0.5. But I would want an exact number instead of a float point approximation, for further use.

To summarize, in this case, how to write -1/2 in test.py? Or is there a way to load a sage package with namespace? Thanks!