python-peps/pep-0001.txt

PEP: 1
Title: PEP Purpose and Guidelines
Version: $Revision$
Last-Modified: $Date$
Author: Barry A. Warsaw, Jeremy Hylton
Status: Active
Type: Informational
Created: 13-Jun-2000
Post-History: 21-Mar-2001, 29-Jul-2002


What is a PEP?

    PEP stands for Python Enhancement Proposal.  A PEP is a design
    document providing information to the Python community, or
    describing a new feature for Python.  The PEP should provide a
    concise technical specification of the feature and a rationale for
    the feature.

    We intend PEPs to be the primary mechanisms for proposing new
    features, for collecting community input on an issue, and for
    documenting the design decisions that have gone into Python.  The
    PEP author is responsible for building consensus within the
    community and documenting dissenting opinions.

    Because the PEPs are maintained as plain text files under CVS
    control, their revision history is the historical record of the
    feature proposal[1].
    

Kinds of PEPs

    There are two kinds of PEPs.  A standards track PEP describes a
    new feature or implementation for Python.  An informational PEP
    describes a Python design issue, or provides general guidelines or
    information to the Python community, but does not propose a new
    feature.  Informational PEPs do not necessarily represent a Python
    community consensus or recommendation, so users and implementors
    are free to ignore informational PEPs or follow their advice.


PEP Work Flow

    The PEP editor, Barry Warsaw <peps@python.org>, assigns numbers
    for each PEP and changes its status.

    The PEP process begins with a new idea for Python.  It is highly
    recommended that a single PEP contain a single key proposal or new
    idea.  The more focussed the PEP, the more successfully it tends
    to be.  The PEP editor reserves the right to reject PEP proposals
    if they appear too unfocussed or too broad.  If in doubt, split
    your PEP into several well-focussed ones.

    Each PEP must have a champion -- someone who writes the PEP using
    the style and format described below, shepherds the discussions in
    the appropriate forums, and attempts to build community consensus
    around the idea.  The PEP champion (a.k.a. Author) should first
    attempt to ascertain whether the idea is PEP-able.  Small
    enhancements or patches often don't need a PEP and can be injected
    into the Python development work flow with a patch submission to
    the SourceForge patch manager[2] or feature request tracker[3].

    The PEP champion then emails the PEP editor <peps@python.org> with
    a proposed title and a rough, but fleshed out, draft of the PEP.
    This draft must be written in PEP style as described below.

    If the PEP editor approves, he will assign the PEP a number, label
    it as standards track or informational, give it status 'draft',
    and create and check-in the initial draft of the PEP.  The PEP
    editor will not unreasonably deny a PEP.  Reasons for denying PEP
    status include duplication of effort, being technically unsound,
    not providing proper motivation or addressing backwards
    compatibility, or not in keeping with the Python philosophy.  The
    BDFL (Benevolent Dictator for Life, Guido van Rossum) can be
    consulted during the approval phase, and is the final arbitrator
    of the draft's PEP-ability.

    If a pre-PEP is rejected, the author may elect to take the pre-PEP
    to the comp.lang.python newsgroup (a.k.a. python-list@python.org
    mailing list) to help flesh it out, gain feedback and consensus
    from the community at large, and improve the PEP for
    re-submission.

    The author of the PEP is then responsible for posting the PEP to
    the community forums, and marshaling community support for it.  As
    updates are necessary, the PEP author can check in new versions if
    they have CVS commit permissions, or can email new PEP versions to
    the PEP editor for committing.

    Standards track PEPs consists of two parts, a design document and
    a reference implementation.  The PEP should be reviewed and
    accepted before a reference implementation is begun, unless a
    reference implementation will aid people in studying the PEP.
    Standards Track PEPs must include an implementation - in the form
    of code, patch, or URL to same - before it can be considered
    Final.

    PEP authors are responsible for collecting community feedback on a
    PEP before submitting it for review.  A PEP that has not been
    discussed on python-list@python.org and/or python-dev@python.org
    will not be accepted.  However, wherever possible, long open-ended
    discussions on public mailing lists should be avoided.  Strategies
    to keep the discussions efficient include, setting up a separate
    SIG mailing list for the topic, having the PEP author accept
    private comments in the early design phases, etc.  PEP authors
    should use their discretion here.

    Once the authors have completed a PEP, they must inform the PEP
    editor that it is ready for review.  PEPs are reviewed by the BDFL
    and his chosen consultants, who may accept or reject a PEP or send
    it back to the author(s) for revision.

    Once a PEP has been accepted, the reference implementation must be
    completed.  When the reference implementation is complete and
    accepted by the BDFL, the status will be changed to `Final.'

    A PEP can also be assigned status `Deferred.'  The PEP author or
    editor can assign the PEP this status when no progress is being
    made on the PEP.  Once a PEP is deferred, the PEP editor can
    re-assign it to draft status.

    A PEP can also be `Rejected'.  Perhaps after all is said and done
    it was not a good idea.  It is still important to have a record of
    this fact.

    PEPs can also be replaced by a different PEP, rendering the
    original obsolete.  This is intended for Informational PEPs, where
    version 2 of an API can replace version 1.

    PEP work flow is as follows:

        Draft -> Accepted -> Final -> Replaced
          ^
          +----> Rejected
          v
        Deferred

    Some informational PEPs may also have a status of `Active' if they
    are never meant to be completed.  E.g. PEP 1.


What belongs in a successful PEP?

    Each PEP should have the following parts:

    1. Preamble -- RFC822 style headers containing meta-data about the
       PEP, including the PEP number, a short descriptive title
       (limited to a maximum of 44 characters), the names, and
       optionally the contact info for each author, etc.

    2. Abstract -- a short (~200 word) description of the technical
       issue being addressed.

    3. Copyright/public domain -- Each PEP must either be explicitly
       labelled as placed in the public domain (see this PEP as an
       example) or licensed under the Open Publication License[4].

    4. Specification -- The technical specification should describe
       the syntax and semantics of any new language feature.  The
       specification should be detailed enough to allow competing,
       interoperable implementations for any of the current Python
       platforms (CPython, JPython, Python .NET).

    5. Motivation -- The motivation is critical for PEPs that want to
       change the Python language.  It should clearly explain why the
       existing language specification is inadequate to address the
       problem that the PEP solves.  PEP submissions without
       sufficient motivation may be rejected outright.

    6. Rationale -- The rationale fleshes out the specification by
       describing what motivated the design and why particular design
       decisions were made.  It should describe alternate designs that
       were considered and related work, e.g. how the feature is
       supported in other languages.

       The rationale should provide evidence of consensus within the
       community and discuss important objections or concerns raised
       during discussion.

    7. Backwards Compatibility -- All PEPs that introduce backwards
       incompatibilities must include a section describing these
       incompatibilities and their severity.  The PEP must explain how
       the author proposes to deal with these incompatibilities.  PEP
       submissions without a sufficient backwards compatibility
       treatise may be rejected outright.

    8. Reference Implementation -- The reference implementation must
       be completed before any PEP is given status 'Final,' but it
       need not be completed before the PEP is accepted.  It is better
       to finish the specification and rationale first and reach
       consensus on it before writing code.

       The final implementation must include test code and
       documentation appropriate for either the Python language
       reference or the standard library reference.


PEP Template

    PEPs are written in plain ASCII text, and should adhere to a
    rigid style.  There is a Python script that parses this style and
    converts the plain text PEP to HTML for viewing on the web[5].
    PEP 9 contains a boilerplate[7] template you can use to get
    started writing your PEP.

    Each PEP must begin with an RFC822 style header preamble.  The
    headers must appear in the following order.  Headers marked with
    `*' are optional and are described below.  All other headers are
    required.

        PEP: <pep number>
        Title: <pep title>
        Version: <cvs version string>
        Last-Modified: <cvs date string>
        Author: <list of authors' real names and optionally, email addrs>
      * Discussions-To: <email address>
        Status: <Draft | Active | Accepted | Deferred | Final | Replaced>
        Type: <Informational | Standards Track>
      * Requires: <pep numbers>
        Created: <date created on, in dd-mmm-yyyy format>
      * Python-Version: <version number>
        Post-History: <dates of postings to python-list and python-dev>
      * Replaces: <pep number>
      * Replaced-By: <pep number>

    The Author: header lists the names, and optionally the email
    addresses of all the authors/owners of the PEP.  The format of the
    author entry must be

        Random J. User <address@dom.ain>

    if the email address is included, and just

        Random J. User

    if the address is not given.  For historical reasons the format
    "address@dom.ain (Random J. User)" may appear in a PEP, however
    new PEPs must use the mandated format above, and it is acceptable
    to change this format when PEPs are updated.

    If there are multiple authors, each should be on a separate line
    following RFC 2822 continuation line conventions.  Note that
    personal email addresses in PEPs will be obscured as a defense
    against spam harvesters.

    Standards track PEPs must have a Python-Version: header which
    indicates the version of Python that the feature will be released
    with.  Informational PEPs do not need a Python-Version: header.

    While a PEP is in private discussions (usually during the initial
    Draft phase), a Discussions-To: header will indicate the mailing
    list or URL where the PEP is being discussed.  No Discussions-To:
    header is necessary if the PEP is being discussed privately with
    the author, or on the python-list or python-dev email mailing
    lists.  Note that email addresses in the Discussions-To: header
    will not be obscured.

    Created: records the date that the PEP was assigned a number,
    while Post-History: is used to record the dates of when new
    versions of the PEP are posted to python-list and/or python-dev.
    Both headers should be in dd-mmm-yyyy format, e.g. 14-Aug-2001.

    PEPs may have a Requires: header, indicating the PEP numbers that
    this PEP depends on.

    PEPs may also have a Replaced-By: header indicating that a PEP has
    been rendered obsolete by a later document; the value is the
    number of the PEP that replaces the current document.  The newer
    PEP must have a Replaces: header containing the number of the PEP
    that it rendered obsolete.


PEP Formatting Requirements

    PEP headings must begin in column zero and the initial letter of
    each word must be capitalized as in book titles.  Acronyms should
    be in all capitals.  The body of each section must be indented 4
    spaces.  Code samples inside body sections should be indented a
    further 4 spaces, and other indentation can be used as required to
    make the text readable.  You must use two blank lines between the
    last line of a section's body and the next section heading.

    You must adhere to the Emacs convention of adding two spaces at
    the end of every sentence.  You should fill your paragraphs to
    column 70, but under no circumstances should your lines extend
    past column 79.  If your code samples spill over column 79, you
    should rewrite them.

    Tab characters must never appear in the document at all.  A PEP
    should include the standard Emacs stanza included by example at
    the bottom of this PEP.

    A PEP must contain a Copyright section, and it is strongly
    recommended to put the PEP in the public domain.

    When referencing an external web page in the body of a PEP, you
    should include the title of the page in the text, with a
    footnote reference to the URL.  Do not include the URL in the body
    text of the PEP.  E.g.

        Refer to the Python Language web site [1] for more details.
        ...
        [1] http://www.python.org

    When referring to another PEP, include the PEP number in the body
    text, such as "PEP 1".  The title may optionally appear.  Add a
    footnote reference that includes the PEP's title and author.  It
    may optionally include the explicit URL on a separate line, but
    only in the References section.  Note that the pep2html.py script
    will calculate URLs automatically, e.g.:

            ...
            Refer to PEP 1 [7] for more information about PEP style
            ...

        References

            [7] PEP 1, PEP Purpose and Guidelines, Warsaw, Hylton
                http://www.python.org/peps/pep-0001.html

    If you decide to provide an explicit URL for a PEP, please use
    this as the URL template:

        http://www.python.org/peps/pep-xxxx.html

    PEP numbers in URLs must be padded with zeros from the left, so as
    to be exactly 4 characters wide, however PEP numbers in text are
    never padded.


Reporting PEP Bugs, or Submitting PEP Updates

    How you report a bug, or submit a PEP update depends on several
    factors, such as the maturity of the PEP, the preferences of the
    PEP author, and the nature of your comments.  For the early draft
    stages of the PEP, it's probably best to send your comments and
    changes directly to the PEP author.  For more mature, or finished
    PEPs you may want to submit corrections to the SourceForge bug
    manager[6] or better yet, the SourceForge patch manager[2] so that
    your changes don't get lost.  If the PEP author is a SF developer,
    assign the bug/patch to him, otherwise assign it to the PEP
    editor.

    When in doubt about where to send your changes, please check first
    with the PEP author and/or PEP editor.

    PEP authors who are also SF committers, can update the PEPs
    themselves by using "cvs commit" to commit their changes.
    Remember to also push the formatted PEP text out to the web by
    doing the following:

    % python pep2html.py -i NUM

    where NUM is the number of the PEP you want to push out.  See

    % python pep2html.py --help

    for details.


Transferring PEP Ownership

    It occasionally becomes necessary to transfer ownership of PEPs to
    a new champion.  In general, we'd like to retain the original
    author as a co-author of the transferred PEP, but that's really up
    to the original author.  A good reason to transfer ownership is
    because the original author no longer has the time or interest in
    updating it or following through with the PEP process, or has
    fallen off the face of the 'net (i.e. is unreachable or not
    responding to email).  A bad reason to transfer ownership is
    because you don't agree with the direction of the PEP.  We try to
    build consensus around a PEP, but if that's not possible, you can
    always submit a competing PEP.

    If you are interested assuming ownership of a PEP, send a message
    asking to take over, addressed to both the original author and the
    PEP editor <peps@python.org>.  If the original author doesn't
    respond to email in a timely manner, the PEP editor will make a
    unilateral decision (it's not like such decisions can be
    reversed. :).


References and Footnotes

    [1] This historical record is available by the normal CVS commands
    for retrieving older revisions.  For those without direct access
    to the CVS tree, you can browse the current and past PEP revisions
    via the SourceForge web site at

    http://cvs.sourceforge.net/cgi-bin/cvsweb.cgi/python/nondist/peps/?cvsroot=python

    [2] http://sourceforge.net/tracker/?group_id=5470&atid=305470

    [3] http://sourceforge.net/tracker/?atid=355470&group_id=5470&func=browse

    [4] http://www.opencontent.org/openpub/

    [5] The script referred to here is pep2html.py, which lives in
        the same directory in the CVS tree as the PEPs themselves.
        Try "pep2html.py --help" for details.

        The URL for viewing PEPs on the web is
        http://www.python.org/peps/

    [6] http://sourceforge.net/tracker/?group_id=5470&atid=305470

    [7] PEP 9, Sample PEP Template
        http://www.python.org/peps/pep-0009.html


Copyright

    This document has been placed in the public domain.



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