PEP 301 – Package Index and Metadata for Distutils
- Richard Jones <richard at python.org>
- Standards Track
This PEP proposes several extensions to the Distutils packaging system . These enhancements include a central package index server, tools for submitting package information to the index and extensions to the package metadata to include Trove  information.
This PEP does not address issues of package dependency. It also does not address storage and download of packages as described in PEP 243. Nor is it proposing a local database of packages as described in PEP 262.
Existing package repositories such as the Vaults of Parnassus , CPAN  and PAUSE  will be investigated as prior art in this field.
Python programmers have long needed a simple method of discovering existing modules and systems available for their use. It is arguable that the existence of these systems for other languages have been a significant contribution to their popularity. The existence of the Catalog-SIG, and the many discussions there indicate that there is a large population of users who recognise this need.
The introduction of the Distutils packaging system to Python simplified the process of distributing shareable code, and included mechanisms for the capture of package metadata, but did little with the metadata save ship it with the package.
An interface to the index should be hosted in the python.org domain, giving it an air of legitimacy that existing catalog efforts do not have.
The interface for submitting information to the catalog should be as simple as possible - hopefully just a one-line command for most users.
Issues of package dependency are not addressed due to the complexity of such a system. PEP 262 proposes such a system, but as of this writing the PEP is still unfinished.
Issues of package dissemination (storage on a central server) are not addressed because they require assumptions about availability of storage and bandwidth that I am not in a position to make. PEP 243, which is still being developed, is tackling these issues and many more. This proposal is considered compatible with, and adjunct to the proposal in PEP 243.
The specification takes three parts, the web interface, the Distutils register command and the Distutils Trove classification.
A web interface is implemented over a simple store. The interface is available through the python.org domain, either directly or as packages.python.org.
The store has columns for all metadata fields. The (name, version) double is used as a uniqueness key. Additional submissions for an existing (name, version) will result in an update operation.
The web interface implements the following commands/interfaces:
- Lists known packages, optionally filtered. An additional HTML page, search, presents a form to the user which is used to customise the index view. The index will include a browsing interface like that presented in the Trove interface design section 4.3. The results will be paginated, sorted alphabetically and only showing the most recent version. The most recent version information will be determined using the Distutils LooseVersion class.
- Displays information about the package. All fields are displayed as plain text. The “url” (or “home_page”) field is hyperlinked.
- Accepts a POST submission of metadata about a package. The
“name” and “version” fields are mandatory, as they uniquely identify
an entry in the index. Submit will automatically determine
whether to create a new entry or update an existing entry. The
metadata is checked for correctness where appropriate - specifically
the Trove discriminators are compared with the allowed set. An
update will update all information about the package based on the
new submitted information.
There will also be a submit/edit form that will allow manual submission and updating for those who do not use Distutils.
- Accepts a POST submission of a PKG-INFO file and performs the same function as the submit interface.
- Registers a new user with the index. Requires username, password
and email address. Passwords will be stored in the index database
as SHA hashes. If the username already exists in the database:
- If valid HTTP Basic authentication is provided, the password and email address are updated with the submission information, or
- If no valid authentication is provided, the user is informed that the login is already taken.
Registration will be a three-step process, involving:
- User submission of details via the Distutils register command or through the web,
- Index server sending email to the user’s email address with a URL to visit to confirm registration with a random one-time key, and
- User visits URL with the key and confirms registration.
- An interface for changing user Role assignments.
- Using a supplied email address as the key, this resets a user’s password and sends an email with the new password to the user.
The submit command will require HTTP Basic authentication, preferably over an HTTPS connection.
The server interface will indicate success or failure of the commands through a subset of the standard HTTP response codes:
|Code||Meaning||Register command implications|
|200||OK||Everything worked just fine|
|400||Bad request||Data provided for submission was malformed|
|401||Unauthorised||The username or password supplied were incorrect|
|403||Forbidden||User does not have permission to update the package information (not Owner or Maintainer)|
Three user Roles will be assignable to users:
- Owns a package name, may assign Maintainer Role for that name. The first user to register information about a package is deemed Owner of the package name. The Admin user may change this if necessary. May submit updates for the package name.
- Can submit and update info for a particular package name.
- Can assign Owner Role and edit user details. Not specific to a package name.
Index Storage (Schema)
The index is stored in a set of relational database tables:
- Lists package names and holds package-level metadata (currently just the stable release version)
- Each package has an entry in releases for each version of the package that is released. A row holds the bulk of the information given in the package’s PKG-INFO file. There is one row for each package (name, version).
- Lists the Trove discriminator text and assigns each one a unique ID.
- Each entry maps a package (name, version) to a discriminator_id. We map to releases instead of packages because the set of discriminators may change between releases.
- Holds information about changes to package information in the index. Changes to the packages, releases, roles, and release_discriminators tables are listed here by package name and version if the change is release-specific.
- Holds our user database - user name, email address and password.
- Maps user_name and role_name to a package_name.
An additional table, rego_otk holds the One Time Keys generated during registration and is not interesting in the scope of the index itself.
Distutils register Command
An additional Distutils command,
register, is implemented which
posts the package metadata to the central index. The register
command automatically handles user registration; the user is presented
with three options:
- login and submit package information
- register as a new packager
- send password reminder email
On systems where the
$HOME environment variable is set, the user
will be prompted at exit to save their username/password to a file
$HOME directory in the file
Notification of changes to a package entry will be sent to all users who have submitted information about the package. That is, the original submitter and any subsequent updaters.
The register command will include a
--verify option which
performs a test submission to the index without actually committing
the data. The index will perform its submission verification checks
as usual and report any errors it would have reported during a normal
submission. This is useful for verifying correctness of Trove
Distutils Trove Classification
The Trove concept of discrimination will be added to the metadata set available to package authors through the new attribute “classifiers”. The list of classifiers will be available through the web, and added to the package like so:
setup( name = "roundup", version = __version__, classifiers = [ 'Development Status :: 4 - Beta', 'Environment :: Console', 'Environment :: Web Environment', 'Intended Audience :: End Users/Desktop', 'Intended Audience :: Developers', 'Intended Audience :: System Administrators', 'License :: OSI Approved :: Python Software Foundation License', 'Operating System :: MacOS :: MacOS X', 'Operating System :: Microsoft :: Windows', 'Operating System :: POSIX', 'Programming Language :: Python', 'Topic :: Communications :: Email', 'Topic :: Office/Business', 'Topic :: Software Development :: Bug Tracking', ], url = 'http://sourceforge.net/projects/roundup/', ... )
It was decided that strings would be used for the classification entries due to the deep nesting that would be involved in a more formal Python structure.
The original Trove specification that classification namespaces be separated by slashes (“/”) unfortunately collides with many of the names having slashes in them (e.g. “OS/2”). The double-colon solution (” :: “) implemented by SourceForge and FreshMeat gets around this limitation.
The list of classification values on the module index has been merged
from FreshMeat and SourceForge (with their permission). This list
will be made available both through the web interface and through the
--list-classifiers option as a text list
which may then be copied to the
setup.py file. The register
--verify option will check classifiers values against
the server’s list.
Unfortunately, the addition of the “classifiers” property is not backwards-compatible. A setup.py file using it will not work under Python 2.1.3. It is hoped that a bug-fix release of Python 2.2 (most likely 2.2.3) will relax the argument checking of the setup() command to allow new keywords, even if they’re not actually used. It is preferable that a warning be produced, rather than a show-stopping error. The use of the new keyword should be discouraged in situations where the package is advertised as being compatible with python versions earlier than 2.2.3 or 2.3.
In the PKG-INFO, the classifiers list items will appear as individual
Name: roundup Version: 0.5.2 Classifier: Development Status :: 4 - Beta Classifier: Environment :: Console (Text Based) . . Classifier: Topic :: Software Development :: Bug Tracking Url: http://sourceforge.net/projects/roundup/
The server is available at:
The code is available from the SourceForge project:
The register command has been integrated into Python 2.3.
Originally, the index server was to return custom headers (inspired by PEP 243):
- Either “success” or “fail”.
- A description of the reason for failure, or additional information in the case of a success.
However, it has been pointed out  that this is a bad scheme to use.
This document has been placed in the public domain.
Anthony Baxter, Martin v. Loewis and David Goodger for encouragement and feedback during initial drafting.
A.M. Kuchling for support including hosting the second prototype.
Greg Stein for recommending that the register command interpret the HTTP response codes rather than custom X-PyPI-* headers.
The many participants of the Distutils and Catalog SIGs for their ideas over the years.
Last modified: 2022-06-14 21:22:20 GMT