Not sure how that's relevant. Everything is written in something else.
Python itself is written in C. The Julia github repo shows Julia 68.2%, C 16.3%, C++ 10.4%, Scheme 3.2%. R is a mix of C, C++, R and some Fortran I think...
It is relevant from the point of view of what a developer is able to achieve without being forced to drop down to a 2nd programming language, aka "2 language syndrome".
And how many Python libraries are just plain wrappers, not really written in Python.
are you suggesting that data scientists use C++ for day to day work? those libraries have first-class wrappers in Python (there is R support, but not at the same level).
Python itself is written in C. The Julia github repo shows Julia 68.2%, C 16.3%, C++ 10.4%, Scheme 3.2%. R is a mix of C, C++, R and some Fortran I think...