Each type types.CodeType constructor changes, a lot of applications break. Python 3.8 added a new parameter which broke for example the Genshi project, just to name one.I propose to add a new CodeType.replace() method, similar to datetime.datetime.replace and namedtuple._replace() for example:$ python3Python 3.7.3 (default, Mar 27 2019, 13:41:07) >>> import datetime>>> d=datetime.datetime.now()>>> d2=d.replace(year=2010)>>> d, d2(datetime.datetime(2019, 5, 24, 11, 25, 3, 839966), datetime.datetime(2010, 5, 24, 11, 25, 3, 839966))>>> import collections>>> Point = collections.namedtuple("Point", "x y")>>> p=Point(1, 2)>>> p2=p._replace(y=3)>>> p, p2(Point(x=1, y=2), Point(x=1, y=3))

> Python 3.8 added a new parameter which broke for example the Genshi projectPablo fixed it in Genshi:https://github.com/edgewall/genshi/pull/19

See alsobpo-37034: "Argument Clinic omits name of keyword-only parameter on _PyArg_BadArgument() call".

Fix in Hypothesis:https://github.com/HypothesisWorks/hypothesis/commit/8f47297fa2e19c426a42b06bb5f8bf1406b8f0f3#diff-a097452b8ffe8323641ccccac335fbf9

ipython fix:https://github.com/ipython/ipython/commit/248128dfaabb33e922b1e36a298fd7ec0c730069

It's not like Python 3.8 is the first type in Python history that code constructor changed.The PyCode_New() function slowly growed from 3 parameters in 1990 to 16 paramters in 2019 :-)History of PyCode_New().New "posonlyargcount" parameter:commit8c77b8cb9188165a123f2512026e3629bf03dc9bAuthor: Pablo Galindo <Pablogsal@gmail.com>Date:   Mon Apr 29 13:36:57 2019 +0100bpo-36540:PEP 570 -- Implementation (GH-12701)New "kwonlyargcount" parameter,bpo-1549670:commit4f72a78684bbfcdc43ceeabb240ceee54706c4b0Author: Guido van Rossum <guido@python.org>Date:   Fri Oct 27 23:31:49 2006 +0000    Jiwon Seo'sPEP 3102 implementation.    See SF#1549670.    The compiler package has not yet been updated.New "freevars" and "cellvars" parameters,PEP 227:commit64949cb753f206c0ca1d83f55d07afd3c179b81aAuthor: Jeremy Hylton <jeremy@alum.mit.edu>Date:   Thu Jan 25 20:06:59 2001 +0000PEP 227 implementation    ...Include/compile.h        Add co_freevars and co_cellvars slots to code objects.        Update PyCode_New() to take freevars and cellvars as argumentsNew "firstlineno" and "lnotab" parameters:commitda4eb5c3b55df9b7d6957ddd0458313102f0a92eAuthor: Guido van Rossum <guido@python.org>Date:   Fri Jan 24 03:43:35 1997 +0000    Instead of emitting SET_LINENO instructions, generate a line number    table which is incorporated in the code object.  This way, the runtime    overhead to keep track of line numbers is only incurred when an    exception has to be reported.New "stacksize" parameter:commit8b993a98db507cc3a75067af4c865ffc8afbada1Author: Guido van Rossum <guido@python.org>Date:   Fri Jan 17 21:04:03 1997 +0000    Add co_stacksize field to codeobject structure, and stacksize argument    to PyCode_New() argument list.  Move MAXBLOCKS constant to conpile.h.        Added accurate calculation of the actual stack size needed by the    generated code.        Also commented out all fprintf statements (except for a new one to    diagnose stack underflow, and one in #ifdef'ed out code), and added    some new TO DO suggestions (now that the stacksize is taken of the TO    DO list).New "argcount", "nlocals", "flags" and "varnames" parameters:commit681d79aaf397850778608f35585d091fa7fe370aAuthor: Guido van Rossum <guido@python.org>Date:   Tue Jul 18 14:51:37 1995 +0000    keyword arguments and faster callsNew "name" parameter:commit9bfef44d97d1ae24e03717e3d59024b44626a9deAuthor: Guido van Rossum <guido@python.org>Date:   Mon Mar 29 10:43:31 1993 +0000    ...    * Added function name to code object.  Print it for code and function      objects.  THIS MAKES THE .PYC FILE FORMAT INCOMPATIBLE (the version      number has changed accordingly)    ...New "filename" parameter:commit3f5da24ea304e674a9abbdcffc4d671e32aa70f1Author: Guido van Rossum <guido@python.org>Date:   Thu Dec 20 15:06:42 1990 +0000    "Compiling" versionThe very first version of the function was:static codeobject *newcodeobject(code, consts, names)  object *code;  object *consts;  object *names;From this commit:commit10dc2e8097e7a431367e72f46ddba91be93aa159Author: Guido van Rossum <guido@python.org>Date:   Sun Nov 18 17:27:39 1990 +0000    Initial revision

> It's not like Python 3.8 is the first type in Python history that code constructor changed.Oops, typo: It's not like Python 3.8 is the first *time* in Python history that the code constructor changed.

Fix in Cloud Pickle:https://github.com/cloudpipe/cloudpickle/commit/b9dc17fc5f723ffbfc665295fafdd076907c0a93

Seebpo-36886 "Failed to construct CodeType on Python-3.8.0a4" for other failures caused by the addition of the "posonlyargcount" parameter to code constructor.

New changeseta9f05d69ccbf3c75cdd604c25094282697789a62 by Victor Stinner in branch 'master':bpo-37032: Add CodeType.replace() method (GH-13542)https://github.com/python/cpython/commit/a9f05d69ccbf3c75cdd604c25094282697789a62

Once Python 3.8 beta1 will be released, it would be interesting to patch all projects that I had to be fixed to handle the new "posonlyargcount" to use the new "replace()" method is available.Maybe even remove the fix for Python 3.8 alpha 4 and only use use replace() on Python 3.8 and newer.

Is there anything more on this issue?

Pablo: "Is there anything more on this issue?"I proposed "Once Python 3.8 beta1 will be released, it would be interesting to patch all projects that I had to be fixed to handle the new "posonlyargcount" to use the new "replace()" method is available."But that only concerns third party project,s no Python directly, so I close the issue :-)

Thanks for this great improvement!Was about to suggest having something more futureproof when noticing this with pdbpp, found this, and submitted PRs to use it for ipython and hypothesis also.

> submitted PRs to use it for ipython and hypothesis alsoCool! Thank you for doing that ;-)