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Python Enhancement Proposals

PEP 241 – Metadata for Python Software Packages

A.M. Kuchling <amk at>
Standards Track

Table of Contents


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

Including Metadata in Packages

The Distutils ‘sdist’ command will be modified to extract the metadata fields from the arguments and write them to a file in the generated zipfile or tarball. This file will be named PKG-INFO and will be placed in the top directory of the source distribution (where the README, INSTALL, and other files usually go).

Developers may not provide their own PKG-INFO file. The “sdist” command will, if it detects an existing PKG-INFO file, terminate with an appropriate error message. This should prevent confusion caused by the PKG-INFO and files being out of sync.

The PKG-INFO file format is a single set of RFC 822 headers parseable by the module. The field names listed in the following section are used as the header names. There’s no extension mechanism in this simple format; the Catalog and Distutils SIGs will aim at getting a more flexible format ready for Python 2.2.


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.


Version of the file format; currently “1.0” is the only legal value here.


Metadata-Version: 1.0


The name of the package.


Name: BeagleVote


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.


Version: 1.0a2

Platform (multiple use)

A comma-separated list of platform specifications, summarizing the operating systems supported by the package. The major supported platforms are listed below, but this list is necessarily incomplete.

POSIX, MacOS, Windows, BeOS, Palm OS.

Binary distributions 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 are not specified in this PEP.


Platform: POSIX, Windows


A one-line summary of what the package does.


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 one hopes that people won’t include their instruction manual as the long-description.)


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.


Keywords: dog puppy voting election

Home-page (optional)

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



Author (optional)

A string containing at a minimum the author’s name. Contact information can also be added, separating each line with newlines.


Author: C. Schultz
        Universal Features Syndicate
        Los Angeles, CA


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.


Author-email: "C. Schultz" <>


A string selected from a short list of choices, specifying the license covering the package. Some licenses result in the software being freely redistributable, so packagers and resellers can automatically know that they’re free to redistribute the software. Other licenses will require a careful reading by a human to determine how the software can be repackaged and resold.

The choices are:

Mozilla PL, "public domain", Python, Qt PL, Zope PL, unknown,
nocommercial, nosell, nosource, shareware, other

Definitions of some of the licenses are:

DFSG The license conforms to the Debian Free Software Guidelines, but does not use one of the other DFSG conforming licenses listed here. More information is available at:
Python Python 1.6 or higher license. Version 1.5.2 and earlier are under the MIT license.
public domain Software is public domain, not copyrighted.
unknown Status is not known
nocommercial Free private use but commercial use not permitted
nosell Free use but distribution for profit by arrangement
nosource Freely distributable but no source code
shareware Payment is requested if software is used
other General category for other non-DFSG licenses

Some of these licenses can be interpreted to mean the software is freely redistributable. The list of redistributable licenses is:

Mozilla PL, "public domain", Python, Qt PL, Zope PL,
nosource, shareware

Note that being redistributable does not mean a package qualifies as free software, ‘nosource’ and ‘shareware’ being examples.


License: MIT


Many changes and rewrites to this document were suggested by the readers of the Distutils SIG. In particular, Sean Reifschneider often contributed actual text for inclusion in this PEP.

The list of licenses was compiled using the SourceForge license list and the CTAN license list compiled by Graham Williams; Carey Evans also offered several useful suggestions on this list.


Last modified: 2022-01-21 11:03:51 GMT