Python script for testing making use of cypari2 if available

cypari2_.py

from sympy import gcd, I

try:
    import cypari2

    pari = cypari2.Pari()
    gen_to_python = cypari2.convert.gen_to_python
except ImportError:
    cypari2 = None

if cypari2 is None:

    def to_sum2sqs(sqrtm1, p):
        return gcd(p, sqrtm1 + I).as_real_imag()

else:

    def to_sum2sqs(sqrtm1, p):
        print("pari")
        [M, V] = pari.halfgcd(sqrtm1, p)
        return gen_to_python(V[1]), gen_to_python(M[1, 0])


def to_sqrtm1(xy, p):
    return xy[0] * pow(xy[1], -1, p) % p

Type "help", "copyright", "credits" or "license" for more information.
>>> from cypari2_ import *
>>> to_sqrtm1((6, -5), 61)
11
>>> to_sum2sqs(11, 61)
pari
(6, -5)
>>> to_sqrtm1(to_sum2sqs(11, 61), 61)
pari
11
>>> to_sum2sqs(to_sqrtm1((6, -5), 61), 61)
pari
(6, -5)
>>> 

Does not neccessarily result in identity:

>>> to_sum2sqs(to_sqrtm1((5, 6), 61), 61)
pari
(6, -5)
>>>