python-peps/pep-0345.txt

PEP: 345
Title: Metadata for Python Software Packages 1.2
Version: $Revision$
Last-Modified: $Date$
Author: Richard Jones <richard@python.org>
Discussions-To: Distutils SIG
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 28-Apr-2005
Python-Version: 2.5
Post-History: 
Replaces: 314


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", "Requires-External", "Requires-Dist",
"Provides-Dist", and "Obsoletes-Dist".  This version also updates the
"Metadata-Version" field, and adds new fields, "Maintainer" and
Maintainer-email".


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  must be in the format specified in `PEP 386`_.

    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@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@example.com>

Maintainer (optional)
    A string containing the maintainer's name at a minimum; additional
    contact information may be provided.
    
    Note that this field is intended for use when a package is being
    maintained by someone other than the original author:  it should be
    omitted if it is identical to ``Author``.

    Example::

        Maintainer: C. Schultz, Universal Features Syndicate,
                Los Angeles, CA <cschultz@peanuts.example.com>

Maintainer-email (optional)
    A string containing the maintainer's e-mail address.  It can contain
    a name and e-mail address in the legal forms for a RFC-822
    ``From:`` header.

    Note that this field is intended for use when a package is being
    maintained by someone other than the original author:  it should be
    omitted if it is identical to ``Author-email``.

    Example::

        Maintainer-email: "C. Schultz" <cschultz@example.com>

License (optional)
    Text indicating the license covering the package where the license
    is not a selection from the "License" Trove classifiers. See
    "Classifier" below.  This field may also be used to specify a
    particular version of a licencse which is named via the ``Classifier``
    field, or to indicate a variation or exception to such a license.

    Examples::

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

        License: GPL version 3, excluding DRM provisions

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.

    Examples::

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

    Note:  this field is now deprecated in favor of ``Requires-Dist``.

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.

    Examples::

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

    Note:  this field is now deprecated in favor of ``Provides-Dist``.

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

    Note:  this field is now deprecated in favor of ``Obsoletes-Dist``.

Requires-Dist (multiple use)
    Each entry contains a string naming some other distutils
    project required by this package.

    The format of a requirement string is identical to that of a
    distutils project name (e.g., as found in the ``Name:`` field.
    optionally followed by a version declaration within parentheses.

    The distutils project names should correspond to names as found
    on the `Python Package Index`_.

    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 specified in `PEP 386`_.
    If no operator is provided with a version, the "==" operator 
    is used by default.

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

    Examples::

        Requires-Dist: pkginfo
        Requires-Dist: PasteDeploy
        Requires-Dist: zope.interface (>3.5.0)

Provides-Dist (multiple use)
    Each entry contains a string naming a distutlis project which
    is contained within this distribution.  This field *must* include
    the project identified in the ``Name`` field.

    A distribution may provide additional names, e.g. to indicate that
    multiple projects have been bundled together.  For instance, source
    distributions of the ``ZODB`` project have historically included
    the ``transaction`` project, which is now available as a separate
    distribution.  Installing such a source distribution satisfies
    requirements for both ``ZODB`` and ``transaction``.

    A distribution may also provide a "virtual" project name, which does
    not correspond to any separately-distributed project:  such a name
    might be used to indicate an abstract capability which could be supplied
    by one of multiple projects.  E.g., multiple projects might supply
    RDBMS bindings for use by a given ORM:  each project might declare
    that it provides ``ORM-bindings``, allowing other projects to depend
    only on having at most one of them installed.
 
    A version declaration may be supplied (without a comparison
    operator); the distribution's version number will be implied if none
    is specified.  Version numbers must be in the format specified in
    `PEP 386`_.

    Examples::

        Provides-Dist: OtherPackage
        Provides-Dist: AnotherPackage (3.4)
        Provides-Dist: virtual_package

Obsoletes-Dist (multiple use)
    Each entry contains a string describing a distutils project which
    this package renders obsolete, meaning that the two packages
    should not be installed at the same time.
    
    Version declarations can be supplied.  Version numbers must be in the
    format specified in `PEP 386`_.

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

    Examples::

        Obsoletes-Dist: Gorgon
        Obsoletes-Dist: OtherPackage (<3.0)

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 "!=". If no operator is provided with a version,
    the "==" operator is used by default.

    Version numbers must be in the format specified in `PEP 386`_.

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

    Examples::

      Requires-Python: >2.1
      Requires-Python: >=2.3.4
      Requires-Python: 2.5, 2.6

Requires-External (multiple use)
    Each entry contains a string describing some dependency in the
    system that the package is to be used.  This field is intended to
    serve as a hint to downstream package maintainers, and has no
    semantics which are meaningful to the ``distutils`` package.

    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 "!=".  Because they
    refer to non-Python software releases, version numbers for
    this field are **not** required to conform to the format
    specified in `PEP 386`_:  they should correspond to the
    version scheme used by the external dependency.

    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 `Python Package Index`_ database:  see
    `External References Registry`_ below for a description of how
    the allowed values are managed.

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

    Examples::

      Requires-External: C
      Requires-External: libpng (>=1.5)


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

    Examples::

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

Version Specifiers
==================

The specification for distribution version specifiers has been moved to
`PEP 386`_.


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

Stores in the `Python Package Index`_ 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

Environment markers
===================

An **environment marker** is a marker that can be added at the end of a
field after a semi-colon (';'), to add a condition about the execution
environment.

Here are some example of fields using such markers::

   Requires-Dist: pywin32, bar > 1.0; sys.platform == 'win32'
   Obsoletes-Dist: pywin31; sys.platform == 'win32'
   Requires-Dist: foo; os.machine == 'i386'
   Requires-Dist: bar; python_version == '2.4' or python_version == '2.5'
   Requires-External: libxslt; 'linux' in sys.platform

These markers are using a micro-language that can be interpreted using a 
function ``interpret_marker`` provided in the ``distutils.util`` module
in the stdlib::

    >>> from distutils.util import
    >>> interpret_marker("sys.platform == 'win32'")
    True

Depending if the execution environment meets the requirements, the function 
will return True or False.

The micro-language behind this is the simplest possible: it compares only
strings, with the ``==`` and ``in`` operators (and their opposites), and
with the ability to combine expressions. It makes it also easy to understand
to non-pythoneers.

The pseudo-grammar is ::

    EXPR [in|==|!=|not in] EXPR [or|and] ...

where ``EXPR`` belongs to any of those:

- python_version = '%s.%s' % (sys.version_info[0], sys.version_info[1])
- os.name = os.name
- sys.platform = sys.platform
- platform.version = platform.version()
- platform.machine = platform.machine()
- a free string, like ``2.4``, or ``win32``

Notice that ``in`` is restricted to strings, meaning that it is not possible
to use other sequences like tuples or lists on the right side.

The fields that benefit from this marker are:

- Requires-Python
- Requires-External
- Requires-Dist
- Provides-Dist
- Obsoletes-Dist
- Classifier

Summary of Differences From PEP 314
===================================

* Metadata-Version is now 1.2.

* Added the environment markers.

* Added fields:

  - Maintainer
  - Maintainer-email
  - Requires-Python
  - Requires-External
  - Requires-Dist
  - Provides-Dist
  - Obsoletes-Dist

* Deprecated fields:

  - Requires (in favor of Requires-Dist)
  - Provides (in favor of Provides-Dist)
  - Obsoletes (in favor of Obsoletes-Dist)


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.

.. [1] reStructuredText markup:
   http://docutils.sourceforge.net/

.. _`Python Package Index`: http://pypi.python.org/pypi/

.. _`PEP 386`: http://www.python.org/dev/peps/pep-0386



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.

Tres Seaver, Jim Fulton, Marc-André Lemburg, Tarek Ziadé and other people at 
the Distutils-SIG have contributed to the new updated version.


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