SageMath? I never used it but I hear it passing by as alternative.
(And this one popped in Google as second when I just searched; https://github.com/Mathics3/mathics-core)
(And this one popped in Google as second when I just searched; https://github.com/Mathics3/mathics-core)
Unfortunately, SageMath is not directly usable as a Python package.
That's where passagemath [0] comes in, making the rich ecosystem of SageMath available to Python devs, one package at a time.