The %cython mode for Sage notebooks (which I wrote in I think 2008??) does precisely that by generating a random-named Python shared object libary and importing

The %cython mode for Sage notebooks (which I wrote in I think 2008??) does precisely that by generating a random-named Python shared object libary and importing it into the runnig Python process after each evaluation. There's a similar (%%cython?) mode for Jupyter notebooks.