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:maxdepth: 5

communication-channels
lang-changes
development-cycle
stdlib
extension-modules
c-api
lang-changes
grammar
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154 changes: 116 additions & 38 deletions developer-workflow/lang-changes.rst
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.. _lang-changes:
.. _langchanges:

Changing the Python language
============================
On occasion people come up with an idea on how to change or improve Python as a
programming language. This document is meant to explain exactly what changes
have a reasonable chance of being considered and what the process is to propose
changes to the language.
Changing Python
===============

On occasion people come up with an idea for changing or improving Python.
This page explains how to explore change proposals and what changes
have a reasonable chance of being considered.

What qualifies

Considerations
--------------
First and foremost, it must be understood that changes to the Python
programming language are difficult to make. When the language changes,
**every** Python programmer already in existence and all Python programmers to

First, understand that changes to Python
are difficult to make. When the language changes,
**every** Python programmer and all Python programmers to
come will end up eventually learning about the change you want to propose.
Books will need updating, code will be changed, and a new way to do things will
need to be learned. Changes to the Python programming language are never taken
need to be learned. Changes to Python are never taken
lightly.

Because of the seriousness that language changes carry, any change must be
beneficial to a large proportion of Python users. If the change only benefits a
Backward compatibility is a significant concern. Existing Python code has to
continue to work. There are exceptions to this rule, but they are very rare
and are only allowed when the benefits of the change greatly outweigh the costs
of breaking existing code.

Because of the seriousness of changing the language, any change must be
beneficial to a many Python users. If the change only helps a
small percentage of Python developers then the change will not be made. A good
way to see if your idea would work for a large portion of the Python community
is to ask in the `Ideas Discourse category`_. You can also
go through Python's stdlib and find examples of code which would benefit from
your proposed change (which helps communicate the usefulness of your change to
others). For further guidance, see :ref:`suggesting-changes`.
is to ask in the `Ideas Discourse category <ideas_>`_. You can also
look in Python's standard library to find examples of code which would benefit from
your proposed change. This can also help communicate the usefulness of your change to
others.

Your proposed change also needs to be *Pythonic*. While only the Steering
Council can truly classify something as Pythonic, you can read the
:pep:`Zen of Python <20>` for guidance.
For all of these reasons, most proposed changes to Python are rejected. This
doesn't mean you shouldn't suggest them. It can be useful to explore
alternatives and to get feedback from the community. Just be aware that
getting a change accepted is difficult. Don't take it personally.


.. index::
Expand All @@ -41,25 +48,97 @@ Council can truly classify something as Pythonic, you can read the
Suggesting new features and language changes
--------------------------------------------

The `Ideas Discourse category`_
is specifically intended for discussion of new features and language changes.
Please don't be disappointed if your idea isn't met with universal approval:
as the :pep:`long list of Withdrawn and Rejected PEPs
<0#rejected-superseded-and-withdrawn-peps>`
in the :pep:`PEP Index <0>` attests,
and as befits a reasonably mature programming language,
getting significant changes into Python isn't a simple task.
Proposing a change involves the following steps:

- Describe your idea.

- Engage in discussion about the idea.

- Rarely, the idea will advance to a formal proposal stage.


Describe your idea
^^^^^^^^^^^^^^^^^^

The `Ideas Discourse category <ideas_>`_ is specifically intended for discussion
of new features and language changes. Make your proposal as a `new topic
<ideas_>`_ there.

Your proposal needs to be **detailed**. Describe the change you want to make,
why you want to make it, and what benefits it will bring to Python users. Be
specific. Show that you have considered the effect of the change on existing
code.

Some things you should **not** do:

- **Don't** format your idea as a PEP. It's good to use the PEP template as a
guide for what information to include, but don't try to write a full PEP
until the idea has been accepted for further consideration.

- **Don't** create a list of proposed changes. Each idea needs its own
discussion. Proposing a change is significant work. You will need to spend
time on each proposal.

When justifying your idea, these are not good reasons to make a change:

- "Other languages work this way." Languages are different. What works well
in one language may not work well in Python, or Python may already have a
way to do a similar thing.

- "It would be nice." This is too vague. Be specific about the benefits
your change will bring, and consider the costs as well.

Some things you **should** do:

- Research whether your idea has been proposed before. There are many
suggestions that have been made and rejected in the past. If your idea has a
history, read the discussion to see why it was rejected. Previously rejected
ideas are especially unlikely to get accepted. If you can address the
concerns raised in the previous discussion, mention that in your proposal.

- Read other ideas to see how they are presented. This will help you flesh out
your proposal.

- Read other ideas to understand the kinds of concerns that are raised and
objections that must be answered. Your proposal will be stronger if you can
address these concerns up front.


Engage in Discussion
^^^^^^^^^^^^^^^^^^^^

Once you post your proposal, people will respond. You need to continue
the discussion, answer questions, and address objections. This is an important
part of the process. Other people's perspectives will help explore the full
impact of the idea and find strengths or weaknesses you may not have
considered.

You will get push-back. Don't be disappointed, and don't take it personally.
As the long list of :pep:`Withdrawn and Rejected PEPs
<0#rejected-superseded-and-withdrawn-peps>` in the :pep:`PEP Index <0>`
attests, and as befits a mature programming language, getting significant
changes into Python isn't a simple task.

Engage in good faith. The goal of the discussion is to find the best balance
between competing concerns. If your idea has merit, the discussion will help
refine it and make it stronger. If your idea has flaws, the discussion will
help identify them so you can address them or move on. Keep the discussion
productive and focused on the issues, not on personalities.

It's especially useful to get core team members involved in the discussion.
Sometimes they will differ in opinion, or merely be unconvinced. When there
isn't a clear positive sentiment, the `Status Quo Wins a Stalemate`_.

Even if your idea is not accepted, the discussion can help you and others
understand the design of Python better, and help inform future propoosals.

If the idea is reasonable, someone will suggest posting it as a feature
request on the `issue tracker`_, or, for larger changes,
writing it up as PEP following the :ref:`lang-changes-pep-process`.

Sometimes core developers will differ in opinion,
or merely be collectively unconvinced.
When there isn't an obvious victor, then the `Status Quo Wins a Stalemate`_.
Formal proposal
^^^^^^^^^^^^^^^

For some examples on language changes that were accepted,
see `Justifying Python Language Changes`_.
If the idea gets positive discussion, someone will suggest posting it as a
feature request on the `issue tracker`_, or, for larger changes, writing it up
as PEP following the :ref:`lang-changes-pep-process`. Congratulations!


.. index:: PEP process
Expand All @@ -83,6 +162,5 @@ to inform others who may propose a similar language change in the future.


.. _issue tracker: https://github.com/python/cpython/issues
.. _Ideas Discourse category: https://discuss.python.org/c/ideas/6
.. _ideas: https://discuss.python.org/c/ideas/6
.. _Status Quo Wins a Stalemate: https://www.curiousefficiency.org/posts/2011/02/status-quo-wins-stalemate.html
.. _Justifying Python Language Changes: https://www.curiousefficiency.org/posts/2011/02/justifying-python-language-changes.html
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