[vog]

I used to use a lot of SymPy, but finally switched to Sage. This is Python as well, but has some syntax extensions and sensible defaults that reduce many quirks of Python. For example, you can write 1/2 instead of of Rational(1,2) and a^b instead of ab.

Moreover, Sage integrates lots of other libraries seamlessly. I remember doing lots of polynomial calculations and groebner basis stuff, and generating Singular script from Python seemed to be very elegant in the beginning. However, this quickly showed severe drawbacks. With Sage this all became easy and seamless again.

[mikorym]

There was a post about Sage not long ago that it is used commonly among cryptographers.

As an aside, the statistical libraries and conveniences of R ("missing value" is a data type; every object is an array meaning you can call functions on arbitrary arrays) are the only reason that I still use R for some niche applications. I wonder whether pandas or something like Sage will actually take over this functionality. My impression is that the packages in R are so isolated (in a somewhat good sense) for a niche application that they are both difficult to emulate in Python and happen to keep on working long after they were written (and not necessarily maintained).