There isn't a productive -ista suffix in English; it occurs in loanwords, or words created to ironically mimic a foreign language in the Romance family ("fashionista").

The -ista suffix in some European languages which have it is not universally feminine.

  English                    Slovak                       Italian
                        (m)         (f)              (m)          (f)

  fascist             fašista     fašistka         fascista     fasciste
  racist              rasista     rasistka         razzista     razziste

See here: https://www.etymonline.com/word/-ist

https://en.wiktionary.org/wiki/-ista

The -ista suffix from Latin, where it is a masculine, appearing in that form in a number of Romance languages, and in French as -iste, is masculine. The English -ist comes from the Latin -ista.

You assume wrongly, Pythonista has been in use for both genders for a long time (more than a decade).