CPython

Eli Bendersky's article on Symbol tables lists the four main actions of the CPython front-end as follows:

• (1) Parse source code into a parse tree
• (2) Transform parse tree into an Abstract Syntax Tree
• (3) Transform AST into a Control Flow Graph
• (4) Emit bytecode based on the Control Flow Graph

The Global Interpreter Lock (GIL) makes sure that at any given time only one Python thread executes bytecode.

sys.setswitchinterval() determines how frequently Python's virtual machine switches between threads.

See also the threading module.

CPython's development model can be enabled with the command line option -X dev. This changes the following features:

• Add default warning filter, as -W default
• Install debug hooks on memory allocators: see the PyMem_SetupDebugHooks() C function
• Enable the faulthandler module to dump the Python traceback on a crash
• Enable asyncio debug mode
• Set the dev_mode attribute of sys.flags to True
• io.IOBase destructor logs close() exceptions

Pyodide is CPython port to WebAssembly/Emscripten. It can be tried out here.

PyPy is an alternative for CPython.

Don't confuse CPython with Cython.