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@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>

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 [2] 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 [2] 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.

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.