An Insider Look at CPython: The "Compiler-Interpreter"

A run-of-the-mill Python programmer may not necessarily think about CPython on a day-to-day basis. 

But CPython is an interesting thing to think about.

It is the reference implementation for Python, written in C and Python. C was used in theory to make portability easier - it's also more efficient (so there's no C++ or STL in there).

CPython is both a compiler and an interpreter. Python code is compiled (into bytecode) before being interpreted.  So you can think of it as a "compiler-interpreter".

One (potentially) painful feature of CPython is the Global Interpreter Lock (GIL) - and the GIL is used on each interpreter process - which means effectively only one thread can run at any one time (more explicitly, only one thread can process Python bytecode at any one time). While this simplifies the implementation, it becomes a bottleneck for CPU-intensive tasks.

Concurrency can be achieved by having multiple Python processes (which have by extension, multiple interpreter processes) and enable inter-process communication.  The Python multiprocessing module aims to make this paradigm simpler to implement.  This is however not available on mobile platforms or WebAssembly platforms.