I've never used cython before. Is it 1-to-1 with standard Python? If so, can you do development using the regular Python binary, and leave the compilation step as a pre-commit operation?
So if you change some of your Cython code, for it to be used at runtime you need to invoke the Cython build tools to rebuild the new version of your python native module.
I usually use Cython for a small core of compute heavy operations, and leave the rest of the project as pure python. That way I only need to rebuild Cython code if I change something inside that small core.
> Is it 1-to-1 with standard Python?
Not for the best speedups, no.
E.g. you might be able to get a modest speedup, say 50%, taking a pure python file, renaming it to *.pyx, and getting Cython to compile it. But that's not why I use Cython. I use it when I have compute-heavy code that I want to run at native speed (think matrix-vector product type stuff), by carefully rewriting in Cython, thinking carefully about memory allocation, data structures (prefer C arrays!) and performance, it is fairly achievable to get a 500x speedup.
Cython relies on you writing specialised Cython code that is quite close to C code -- strongly typed Cython variables work like statically typed C variables, not dynamically typed Python names. You end up with Cython code that cannot be executed as if it were normal Python code by a python interpreter.
But, Python code can usually not be executed very efficiently, whereas Cython can translate small loops of strongly-typed numeric code into small loops of strongly-typed C code, which can often compile to very small loops of native CPU instructions, which then run blazing fast.
Under the hood, Cython works by translating the not-quite-python code into C code that uses the python interpreter's C extension API. Then it compiles the C code into a python native module using a C compiler.