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: Accepted
Type: Standards Track
Content-Type: text/x-rst
Created: 28-Apr-2005
Python-Version: 2.5
Post-History:


Abstract
========

This PEP describes a mechanism for adding metadata to Python distributions.
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 changes the
"Platform" field. Three new fields were also added: "Maintainer",
"Maintainer-email" and "Project-URL".

Last, this new version also adds `environment markers`.

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; "1.2" is the only legal value.

Example::

    Metadata-Version: 1.2


Name
::::

The name of the distributions.

Example::

    Name: BeagleVote


Version
:::::::

A string containing the distribution's version number.  This
field  must be in the format specified in PEP 386.

Example::

    Version: 1.0a2


Platform (multiple use)
:::::::::::::::::::::::

A Platform specification describing an operating system supported by
the distribution which is not listed in the "Operating System" Trove classifiers.
See "Classifier" below.

Examples::

    Platform: ObscureUnix
    Platform: 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 distribution 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 distribution does.

Example::

    Summary: A module for collecting votes from beagles.


Description (optional)
::::::::::::::::::::::

A longer description of the distribution 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.

To support empty lines and lines with indentation with respect to
the RFC 822 format, any CRLF character has to be suffixed by 7 spaces
followed by a pipe ("|") char. As a result, the Description field is
encoded into a folded field that can be interpreted by RFC822
parser [2]_.

Example::

    Description: This project provides powerful math functions
            |For example, you can use `sum()` to sum numbers:
            |
            |Example::
            |
            |    >>> sum(1, 2)
            |    3
            |

This encoding implies that any occurences of a CRLF followed by 7 spaces
and a pipe char have to be replaced by a single CRLF when the field is unfolded
using a RFC822 reader.


Keywords (optional)
:::::::::::::::::::

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

Example::

    Keywords: dog puppy voting election


Home-page (optional)
::::::::::::::::::::

A string containing the URL for the distribution'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 distribution
can be downloaded.  (This means that the URL can't be something like
".../BeagleVote-latest.tgz", but instead must be ".../BeagleVote-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 (optional)
:::::::::::::::::::::::

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.

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 project 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 project 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 distribution 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 distribution.  Classifiers are described in PEP 301 [2].

Examples::

    Classifier: Development Status :: 4 - Beta
    Classifier: Environment :: Console (Text Based)


Requires-Dist (multiple use)
::::::::::::::::::::::::::::

Each entry contains a string naming some other distutils
project required by this distribution.

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`_.

Version declarations must follow the rules described in
`Version Specifiers`_

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 Distutils 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 and must follow the rules described
in `Version Specifiers`_. The distribution's version number will be implied
if none is specified.

Examples::

    Provides-Dist: OtherProject
    Provides-Dist: AnotherProject (3.4)
    Provides-Dist: virtual_package


Obsoletes-Dist (multiple use)
:::::::::::::::::::::::::::::

Each entry contains a string describing a distutils project's distribution
which this distribution renders obsolete, meaning that the two projects
should not be installed at the same time.

Version declarations can be supplied.  Version numbers must be in the
format specified in `Version Specifiers`_.

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: OtherProject (<3.0)


Requires-Python
:::::::::::::::

This field specifies the Python version(s) that the distribution is
guaranteed to be compatible with.

Version numbers must be in the format specified in `Version Specifiers`_.

Examples::

    Requires-Python: 2.5
    Requires-Python: >2.1
    Requires-Python: >=2.3.4
    Requires-Python: >=2.5,<2.7


Requires-External (multiple use)
::::::::::::::::::::::::::::::::

Each entry contains a string describing some dependency in the
system that the distribution is to be used.  This field is intended to
serve as a hint to downstream project maintainers, and has no
semantics which are meaningful to the ``distutils`` distribution.

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

Version numbers must be in the format specified in `Version Specifiers`_.

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.

Notice that there's is no particular rule on the strings to be used.

Examples::

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


Project-URL (multiple-use)
::::::::::::::::::::::::::

A string containing a browsable URL for the project and a label for it,
separated by a comma.

Example::

    Bug Tracker, http://bitbucket.org/tarek/distribute/issues/

The label is a free text limited to 32 signs.


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

Version specifiers are a series of conditional operators and
version numbers, separated by commas.  Conditional operators
must be one of "<", ">", "<=", ">=", "==" and "!=".

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 comma (",") is equivalent to the **and** operator.

Each version number must be in the format specified in PEP 386.

When a version is provided, it always includes all versions that
starts with the same value. For example the "2.5" version of Python
will include versions like "2.5.2" or "2.5.3". Pre and post releases
in that case are excluded. So in our example, versions like "2.5a1" are
not included when "2.5" is used. If the first version of the range is
required, it has to be explicitly given. In our example, it will be
"2.5.0".

Notice that some projects might omit the ".0" prefix for the first release
of the "2.5.x" series:

- 2.5
- 2.5.1
- 2.5.2
- etc.

In that case, "2.5.0" will have to be explicitly used to avoid any confusion
between the "2.5" notation that represents the full range. It is a recommended
practice to use schemes of the same length for a series to completely avoid
this problem.

Some Examples:

- ``Requires-Dist: zope.interface (3.1)``: any version that starts with 3.1,
  excluding post or pre-releases.
- ``Requires-Dist: zope.interface (3.1.0)``: any version that starts with
  3.1.0, excluding post or pre-releases. Since that particular project doesn't
  use more than 3 digits, it also means "only the 3.1.0 release".
- ``Requires-Python: 3``: Any Python 3 version, no matter wich one, excluding
  post or pre-releases.
- ``Requires-Python: >=2.6,<3``: Any version of Python 2.6 or 2.7, including
  post releases of 2.6, pre and post releases of 2.7. It excludes pre releases
  of Python 3.
- ``Requires-Python: 2.6.2``: Equivalent to ">=2.6.2,<2.6.3". So this includes
  only Python 2.6.2. Of course, if Python was numbered with 4 digits, it would
  have include all versions of the 2.6.2 series.
- ``Requires-Python: 2.5.0``: Equivalent to ">=2.5.0,<2.5.1".
- ``Requires-Dist: zope.interface (3.1,!=3.1.3)``: any version that starts with
  3.1, excluding post or pre-releases of 3.1 *and* excluding any version that
  starts with "3.1.3". For this particular project, this means: "any version
  of the 3.1 series but not 3.1.3". This is equivalent to:
  ">=3.1,!=3.1.3,<3.2".

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 (>1.0); sys.platform == 'win32'
   Obsoletes-Dist: pywin31; sys.platform == 'win32'
   Requires-Dist: foo (1,!=1.3); platform.machine == 'i386'
   Requires-Dist: bar; python_version == '2.4' or python_version == '2.5'
   Requires-External: libxslt; 'linux' in sys.platform

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])
- python_full_version = sys.version.split()[0]
- 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.

* Changed fields:

  - Platform
  - Author

* Added fields:

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

* 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/

.. [2] RFC 822 Long Header Fields:
   http://www.freesoft.org/CIE/RFC/822/7.htm

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, Martin von Löwis, Tarek Ziadé,
David Lyon and other people at the Distutils-SIG have contributed to the
new updated version.


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