[docs] [issue36896] clarify in types.rst that FunctionTypes & co constructors don't have stable signature

[Matthias Bussonnier]

New submission from Matthias Bussonnier <bussonniermatthias at gmail.com>:

>From bpo-36886, 

IT is unclear the FunctionTypes, CodeTypes ... etc are not stable between python versions, and the recent addition of `:=` change some of the signatures.  


This suggest 2 things: 
 - A CYA sentence in types.rst "These types are not supposed to be instantiated outside of CPython internals and constructor signatures will vary between python versions." or alike
 - As many people don't read online documentation but on the docstring via calling `help()`, to add something similar to all the docstrings of said-objects constructors.

----------
assignee: docs at python
components: Documentation
messages: 342271
nosy: docs at python, mbussonn
priority: normal
severity: normal
status: open
title: clarify in types.rst that FunctionTypes & co  constructors don't have stable signature
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue36896>
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