I made some small contributions to cpython during the 3.14 cycle. The codebase is an interesting mix of modern and “90s style” C code.

I found that agentic coding tools were quite good at answering my architectural questions; even when their answers were only half correct, they usually pointed me in the right direction. (I didn’t use AI to write code and I wonder if agentic tools would struggle with certain aspects of the codebase like, for instance, the Cambrian explosion of utility macros used throughout.)

There's a file on docs.python.org explaining the C api. The rest is pretty straightforward, at least until recently when free threading was introduced (IDK about now). Main hassle is manually having to track reference borrowing etc. Understandable in Python 2, but another tragedy in Python 3.

Great write up, thank you for sharing it! Quick question though, in your first code example (dynamic enum with a metaclass) what is "m" in this line towards the start?

    Py_DECREF(m)

There is.

https://realpython.com/products/cpython-internals-book/ But it's for 3.9 and doesn't cover the massive changes regarding delayed annotations and the GIL updates

The Ruby under a Microscope guy is updating it.

IDK why /InternalDocs/ instead of /Doc/internals/ ? ( `ln -s` works with Mac/Lin/WSL. )

Ideally what's in InternalDocs/ would be built into the docs.python.org docs .

Is it just that markdown support in sphinx is not understood to exist?

Sphinx has native markdown support. Sphinx does not have native MyST Markdown support. To support MyST Markdown in a sphinx-doc project, you must e.g. `pip install myst_parser` and add "myst_parser" to the extensions list in conf.py.

MyST Markdown supports docutils and sphinx RestructuredText roles and directives: https://myst-parser.readthedocs.io/en/latest/syntax/roles-an...

Directive in ReStructuredText .rst:

  .. directivename:: arguments
     :key1: val1
     :key2: val2

   This is
   directive content

  ```{directivename} arguments
  :key1: val1
  :key2: val2
  
  This is
  directive content
  ```

  :role-name:`role content`
  {role-name}`role content`

  .. _label-name:
  (label-name)=

  :ref:`Link title <label-name>`
  {ref}`Link title <label-name>`

Just to name alternatives: Cpython, Pypy, jython, ironpython.

Then, there quite a few python-likes out there.

I wish they would stay precise.

I find it's usually referred to as CPython when discussing something specific to the implementation or internals of Python that don't apply to Pypy, which seems to be the alternative Python implementation with the most traction.

No harm in being explicit right? Tis part of the zen of Python after all.

A lot to unpack there, but the language and the implementation are different.

JavaScript and Node.js are different too.

I feel like when the goal is to talk about the internals of it, then it makes sense to call it CPython.

In general, I never, ever see anyone saying "I will write a CPython script". Everybody says "Python" in my experience... do you see it differently?

EDIT: I don't think that your opinion deserves to be downvoted, though...

Precision in language is important for software engineering.

If we are being very pedantic, languages don't have "speed", only implementations do.

Of course in the real life there are de facto implementations and language features give way to better/worse tradeoffs.

With that out of the way, Python is basically the de facto glue language. It is very often used to provide a scripting API over lower level C libraries. To be ergonomic in this function, CPython (the major implementation) exposed some internal details of its execution model, which C libraries can reach into. This makes it very hard to make more aggressive optimizations, as one example a C library can just increase/decrease the reference count of an object. Another design decision (that got some discussion recently) is the GIL (global interpreter lock) that makes python much less competitive than something like Java. (JS also does a single thread of execution, though there are ways around it).

JS has a different use case, so access to the C world doesn't impose such restrictions on it.

    > Edit: Python has no JIT

JIT-compiler for Python https://pypy.org/

Python enhancement proposal for JIT in CPython https://peps.python.org/pep-0744/

And there are several JIT-compilers for various subsets of Python, usually with focus on numerical code and often with GPU support, for example

Numba https://numba.pydata.org/numba-doc/dev/user/jit.html

Taichi Lang https://github.com/taichi-dev/taichi

> Edit: Python has no JIT

In 3.14 and up you can enable JIT by setting the env var PYTHON_JIT=1

It is not that numpy bypasses public interfaces. It uses documented C APIs. V8, as far as I know, does not have that.

As someone who has many times dived into deep rabbit holes like this (e.g. how does JavaScript's prototype-based class work?), some effective ways to handle this is to ask follow up questions, use web search or ask for references. Deep search also helps. Often it corrects itself or takes back claims that have no basis. At the very least, it provides references that you can read yourself.

Of course, you can't really do all of that on a free plan.

That's far from ideal, but if you are motivated and care about these technical details (which you probably do), you can get pretty good results.

=====

Putting all of this aside, you can sometimes find YouTube videos on obscure channels that talk about these things. Chances are that someone who cares to make a YouTube video about these hardcore topics know what they are talking.

For what it's worth, I really don't get the downvotes. I think it is an interesting question, and it brought interesting answers.

No clue if that's the reason for the downvotes, but maybe next time don't mention ChatGPT and just formulate this as "From what I read, [...]".