remark: I get a similar error from two packages, when experimenting with Python-3.8.0a4 on Windows

````
import asyncio
await asyncio.sleep(0)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
C:\WinP\bd38\bu\WPy64-3800a4\python-3.8.0a4.amd64\lib\site-packages\IPython\core\interactiveshell.py in removed_co_newlocals(function)
    139     CO_NEWLOCALS = 0x0002
    140     code = function.__code__
--> 141     new_code = CodeType(
    142         code.co_argcount,
    143         code.co_kwonlyargcount,

TypeError: an integer is required (got type bytes)
````

or else:

````
import cloudpickle
````

````
import cloudpickle
1 0 1 3 19 b'\x87\x00f\x01d\x01d\x02\x84\x08\x01\x00|\x00\x89\x00d\x00S\x00' (None, <code object <lambda> at 0x000001B36B7D49B0, file "C:\WinP\bd38\bu\WPy64-3800a4\python-3.8.0a4.amd64\lib\site-packages\cloudpickle\cloudpickle.py", line 107>, '_make_cell_set_template_code.<locals>.inner.<locals>.<lambda>') () ('value',) C:\WinP\bd38\bu\WPy64-3800a4\python-3.8.0a4.amd64\lib\site-packages\cloudpickle\cloudpickle.py inner 106 b'\x00\x01\x0c\x01' ('cell',)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-1-316e5ca2d1c8> in <module>
----> 1 import cloudpickle

C:\WinP\bd38\bu\WPy64-3800a4\python-3.8.0a4.amd64\lib\site-packages\cloudpickle\__init__.py in <module>
      1 from __future__ import absolute_import
      2 
----> 3 from cloudpickle.cloudpickle import *
      4 
      5 __version__ = '1.0.0'

C:\WinP\bd38\bu\WPy64-3800a4\python-3.8.0a4.amd64\lib\site-packages\cloudpickle\cloudpickle.py in <module>
    165 
    166 
--> 167 _cell_set_template_code = _make_cell_set_template_code()
    168 
    169 

C:\WinP\bd38\bu\WPy64-3800a4\python-3.8.0a4.amd64\lib\site-packages\cloudpickle\cloudpickle.py in _make_cell_set_template_code()
    146             co.co_lnotab,
    147             co.co_cellvars)
--> 148         return types.CodeType(
    149             co.co_argcount,
    150             co.co_kwonlyargcount,

TypeError: an integer is required (got type bytes)

This is a consequence of PEP 570 that implements positional-only arguments (see issue 36540). Those projects would have to update their code. Good that there are already open bugs for both projects.

If types is not supposed to be stable, could a warning be added at top of https://docs.python.org/3/library/types.html that it should not be considered stable, and/or to CodeType docs to indicate the signature has changed in 3.8 ?

If it is supposed to be stable can the `posonlyargcount` be moved to   be the last argument ?

> If it is supposed to be stable can the `posonlyargcount` be moved to   be the last argument ?

There are other projects that have already added a fix for the new parameter positionally. If we add it to be the last (that still will break the old call) we would break them again.

> and/or to CodeType docs to indicate the signature has changed in 3.8 ?

The documentation never documented the arguments for the code type (probably on purpose), so not sure if adding a notice there will help much:

https://docs.python.org/3.8/library/types.html#types.CodeType

We can maybe add something more clear to the "what's new" section or the changelog.

As a final note, notice that when keyword-only arguments were implemented, the parameter was not added at the end of the constructor:

commit 4f72a78684bbfcdc43ceeabb240ceee54706c4b0
Author: Guido van Rossum <guido@python.org>
Date:   Fri Oct 27 23:31:49 2006 +0000

    Jiwon Seo's PEP 3102 implementation.
    See SF#1549670.
    The compiler package has not yet been updated.


--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -41,7 +41,8 @@ intern_strings(PyObject *tuple)


 PyCodeObject *
-PyCode_New(int argcount, int nlocals, int stacksize, int flags,
+PyCode_New(int argcount, int kwonlyargcount,
+          int nlocals, int stacksize, int flags,
           PyObject *code, PyObject *consts, PyObject *names,
           PyObject *varnames, PyObject *freevars, PyObject *cellvars,
           PyObject *filename, PyObject *name, int firstlineno,

> There are other projects that have already added a fix for the new parameter positionally. If we add it to be the last (that still will break the old call) we would break them again.

Understandable


> The documentation never documented the arguments for the code type (probably on purpose)

Understandable as well, just thinking that a CYA sentence in types.rst: 
"These types are not supposed to be instantiated outside of CPython internals and constructor signatures can vary between python versions.

And maybe the docstrings. I rarely open the documentation on python.org and work most of the time by calling `help()` or `?` in IPython, so having some information saying this is non-public in the docstring would make sens to me. 

I'm happy to do it if it is deemed useful.

>Understandable as well, just thinking that a CYA sentence in types.rst: 
>"These types are not supposed to be instantiated outside of CPython internals and constructor signatures can vary between python versions.
>And maybe the docstrings. I rarely open the documentation on python.org and work most of the time by calling `help()` or `?` in IPython, so having some information saying this is non-public in the docstring would make sens to me. 
>I'm happy to do it if it is deemed useful.

I am +1 to such a sentence, but I think this is a decision that more core devs should agree on. Taking into account previous history (like the linked commit) and
the fact that promising stability on such internal pieces will prevent us from making critical optimizations I assume that others will agree, but I am still important
to know that there is a consensus.

I would recommend opening such PR if you have some time and let others review it as well.

After PR 13255 is merged, let's open a new issue for the notice in types.rst to keep the discussion isolated.

I found a third project that is impacted https://github.com/microsoft/python-language-server/issues/1070.

New changeset 5d23e282af69d404a3430bb95aefe371112817b3 by Pablo Galindo in branch 'master':
bpo-36886: Document changes in code object in What's new section (GH-13255)
https://github.com/python/cpython/commit/5d23e282af69d404a3430bb95aefe371112817b3

Thanks for the update to the what's new Pablo. 

> let's open a new issue for the notice in types.rst to keep the discussion isolated.

See bpo-36896

I created bpo-37032 to add a new CodeType.replace() helper which help projects to be more future-proof (no longer break if CodeType gets yet another parameter).