[Catalog-sig] New PEP, pre-submission RFC

Richard Jones richardjones at optushome.com.au
Fri Apr 29 11:43:32 CEST 2005


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PEP: NNN
Title: Medatadata for Python Software Packages 1.2
Version: $Revision$
Last-Modified: $Date$
Author: Richard Jones <richard at mechanicalcat.net>
Discussions-To: Distutils SIG
Status: Draft
Type: Standards Track
Created: 28-04-2005
Python-Version: 2.5


Abstract
========

This PEP describes a mechanism for adding metadata to Python
packages.  It includes specifics of the field names, and their
semantics and usage.

This document specifies version 1.2 of the metadata format.
Version 1.0 is specified in PEP 241.
Version 1.1 is specified in PEP 314.

Version 1.2 of the metadata format adds a number of optional 
fields designed to make third-party packaging of Python Software
easier. These fields are "Requires-Python" and "Requires-External".
Also, the "Metadata-Version" field is updated.


Fields
======

This section specifies the names and semantics of each of the
supported metadata fields.
 
Fields marked with "(Multiple use)" may be specified multiple
times in a single PKG-INFO file.  Other fields may only occur
once in a PKG-INFO file.  Fields marked with "(optional)" are
not required to appear in a valid PKG-INFO file; all other
fields must be present.

Metadata-Version

    Version of the file format; "1.0", "1.1" and "1.2" are the
    only legal values here.

      Example: 

        Metadata-Version: 1.2

Name

    The name of the package.  

      Example: 

        Name: BeagleVote
      
Version

    A string containing the package's version number.  This
    field should be parseable by one of the Version classes
    (StrictVersion or LooseVersion) in the distutils.version
    module.

    Example: 

        Version: 1.0a2
      
Platform (multiple use)

    A comma-separated list of platform specifications, summarizing
    the operating systems supported by the package which are not
    listed in the "Operating System" Trove classifiers. See
    "Classifier" below.

    Example: 

        Platform: ObscureUnix, RareDOS

Supported-Platform (multiple use)

    Binary distributions containing a PKG-INFO file will use the
    Supported-Platform field in their metadata to specify the OS and
    CPU for which the binary package was compiled.  The semantics of
    the Supported-Platform field are not specified in this PEP.

    Example: 

        Supported-Platform: RedHat 7.2
        Supported-Platform: i386-win32-2791

Summary

    A one-line summary of what the package does.

    Example: 

        Summary: A module for collecting votes from beagles.
    
Description (optional)

    A longer description of the package that can run to several
    paragraphs.  Software that deals with metadata should not assume
    any maximum size for this field, though people shouldn't include
    their instruction manual as the description.  

    The contents of this field can be written using reStructuredText
    markup [1].  For programs that work with the metadata,
    supporting markup is optional; programs can also display the
    contents of the field as-is.  This means that authors should be
    conservative in the markup they use.

    Example: 
    
        Description: This module collects votes from beagles
                    in order to determine their electoral wishes.
                    Do *not* try to use this module with basset hounds;
                    it makes them grumpy.
    
Keywords (optional)

    A list of additional keywords to be used to assist searching
    for the package in a larger catalog.

    Example: 

        Keywords: dog puppy voting election
    
Home-page (optional)

    A string containing the URL for the package's home page.

    Example: 

        Home-page: http://www.example.com/~cschultz/bvote/
    
Download-URL

    A string containing the URL from which this version of the package 
    can be downloaded.  (This means that the URL can't be something like
    ".../package-latest.tgz", but instead must be "../package-0.45.tgz".)
    
Author (optional)

    A string containing the author's name at a minimum; additional
    contact information may be provided.  

    Example: 

        Author: C. Schultz, Universal Features Syndicate,
                Los Angeles, CA <cschultz at peanuts.example.com>
    
Author-email

    A string containing the author's e-mail address.  It can contain
    a name and e-mail address in the legal forms for a RFC-822
    'From:' header.  It's not optional because cataloging systems
    can use the e-mail portion of this field as a unique key
    representing the author.  A catalog might provide authors the
    ability to store their GPG key, personal home page, and other
    additional metadata *about the author*, and optionally the
    ability to associate several e-mail addresses with the same
    person.  Author-related metadata fields are not covered by this
    PEP.  

    Example: 

        Author-email: "C. Schultz" <cschultz at example.com>
    
License
    
    Text indicating the license covering the package where the license
    is not a selection from the "License" Trove classifiers. See
    "Classifier" below.

    Example: 

        License: This software may only be obtained by sending the
                author a postcard, and then the user promises not
                to redistribute it.

Classifier (multiple use)

    Each entry is a string giving a single classification value
    for the package.  Classifiers are described in PEP 301 [2].

    Examples:

      Classifier: Development Status :: 4 - Beta
      Classifier: Environment :: Console (Text Based)
    
Requires (multiple use)
    
    Each entry contains a string describing some other module or
    package required by this package. 

    The format of a requirement string is identical to that of a
    module or package name usable with the 'import' statement,
    optionally followed by a version declaration within parentheses.

    A version declaration is a series of conditional operators and
    version numbers, separated by commas.  Conditional operators
    must be one of "<", ">", "<=", ">=", "==", and "!=".  Version
    numbers must be in the format accepted by the
    distutils.version.StrictVersion class: two or three
    dot-separated numeric components, with an optional "pre-release"
    tag on the end consisting of the letter 'a' or 'b' followed by a
    number.  Example version numbers are "1.0", "2.3a2", "1.3.99", 

    Any number of conditional operators can be specified, e.g.
    the string ">1.0, !=1.3.4, <2.0" is a legal version declaration.

    All of the following are possible requirement strings: "rfc822",
    "zlib (>=1.1.4)", "zope".

    There's no canonical list of what strings should be used; the
    Python community is left to choose its own standards.

    Example: 

        Requires: re
        Requires: sys
        Requires: zlib
        Requires: xml.parsers.expat (>1.0)
        Requires: psycopg
    
Provides (multiple use)

    Each entry contains a string describing a package or module that
    will be provided by this package once it is installed.  These
    strings should match the ones used in Requirements fields.  A
    version declaration may be supplied (without a comparison
    operator); the package's version number will be implied if none
    is specified.

    Example: 

        Provides: xml
        Provides: xml.utils
        Provides: xml.utils.iso8601
        Provides: xml.dom
        Provides: xmltools (1.3)

Obsoletes (multiple use)

    Each entry contains a string describing a package or module
    that this package renders obsolete, meaning that the two packages
    should not be installed at the same time.  Version declarations
    can be supplied.  

    The most common use of this field will be in case a package name
    changes, e.g. Gorgon 2.3 gets subsumed into Torqued Python 1.0.
    When you install Torqued Python, the Gorgon package should be
    removed.
    
    Example:

        Obsoletes: Gorgon

Requires-Python 

    This field specifies the Python version(s) that the package is
    guaranteed to be compatible with. The format of the field is a
    series of conditional operators and version numbers, separated
    by commas.  Conditional operators must be one of "<", ">", "<=",
    ">=", "==", and "!=".  Version numbers must be in the format
    accepted by the distutils.version.StrictVersion class: two or three
    dot-separated numeric components, with an optional "pre-release"
    tag on the end consisting of the letter 'a' or 'b' followed by a
    number.  Example version numbers are "1.0", "2.3a2" and "1.3.99".

    Any number of conditional operators can be specified, e.g.
    the string ">1.0, !=1.3.4, <2.0" is a legal version declaration.

    Example:

      Requires-Python: >2.1
      Requires-Python: >=2.3.4

    XXX This field doesn't take into account possible future
    incompatibilities through deprecation. We could specify that the ">"
    operator only work for up to two releases? This is based on the typical
    deprecation plan that Python usually follows (warning for two releases
    and then error). That is, >=2.3.4 works for 2.3.4, 2.4 and 2.5.

Requires-External (multiple use)
      
    Each entry contains a string describing some dependency in the
    system that the package is to be used.

    The format of a requirement string is a name of an external
    dependency, optionally followed by a version declaration within
    parentheses.

    A version declaration is a series of conditional operators and
    version numbers, separated by commas.  Conditional operators
    must be one of "<", ">", "<=", ">=", "==", and "!=".  Version
    numbers must be in the format accepted by the
    distutils.version.StrictVersion class: two or three
    dot-separated numeric components, with an optional "pre-release"
    tag on the end consisting of the letter 'a' or 'b' followed by a
    number.  Example version numbers are "1.0", "2.3a2", "1.3.99", 

    Any number of conditional operators can be specified, e.g.
    the string ">1.0, !=1.3.4, <2.0" is a legal version declaration.

    The canonical list of what strings are allowed is available
    in the `Cheese Shop`_ database. New names may be added to the
    database either through the web or using the command-line;
    Python community is left to choose its own standards.

    Some dependencies are anticipated to be quite broad, eg. "C",
    indicating a C compiler is required.

    Example: 

      Requires: C
      Requires: libpng


Copyright

    Indicates the party or parties, and the year of copyright
    covering the package.

    Example:

       Copyright: Guido van Rossum, 1991
       Copyright: Python Software Foundation, 2005
       Copyright: Public Domain


External References Registry
============================

Stores in the Cheese Shop database a list of (name, description, URI)
identifying an external reference that may be used as a value in a
Requires-External field.

The name and description are required, but URI is not (as there is no
single useful URI for "C").

Submissions to the registry are open to the community, and may be performed
through the web or using the command-line.

The names in the registry will be created under a first-comes first-wins
basis. Other packagers of Python software (eg. to deb, rpm, etc) should be
able to translate the requires-external field to names in their own
packaging system.

XXX command-line interface needs work, obviously


References
==========

This document specifies version 1.2 of the metadata format.
Version 1.0 is specified in PEP 241.
Version 1.1 is specified in PEP 314.

.. _`Cheese Shop`: http://cheeseshop.python.org/


Copyright
=========

This document has been placed in the public domain.


Acknowledgements
================

Fred Drake, Anthony Baxter and Matthias Klose have all contributed to
the ideas presented in this PEP.


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