[Python-ideas] Decide if `type.__subclasses__` is part of future Python or not

[Joy Diamond]

Greetings,

Currently `type.__subclasses__` is not documented at docs.python.org (and
works in both python 2 & python 3).

I would like to keep `.__subclasses__` and have it documented at
docs.python.org.

Is there a reason it is not documented?

I realize the whole type system is going an overhaul, and the concept of
what is "subclass" of another class is a complicated issue.

See for example: https://github.com/python/typing/issues/135 which talks
about the complexity of deciding subclassing.

I think though, despite the overall, `types.__subclasses__` should be kept
& documented.

Thanks,

Joy Diamond.

1.  The google search: "site:docs.python.org __subclasses__" finds no
instances of the word "__subclasses__"

2.  As for what the function does, it returns the subclasses of a class:

Consider the following program:

class CryptographicActors(object): pass
class Alice(CryptographicActors): pass
class Bob(CryptographicActors): pass

print("CryptographicActors subclases: %s" %
CryptographicActors.__subclasses__())

help(CryptographicActors.__subclasses__)

3.  It properly prints out:

CryptographicActors subclases: [<class '__main__.Alice'>, <class
'__main__.Bob'>]

Showing the two subclasses (`Alice` and `Bob`)

4. The internal documentation explains "__subclasses__() -> list of
immediate subclasses"

To fully figure out what it did, I had to read the source code to Python --
which really is not the best way to figure out what a function does; hence
the request to document it (and indicate it's future existence in python)
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