PEP 423 – Naming conventions and recipes related to packaging

PEP

423

Title

Naming conventions and recipes related to packaging

Version

$Revision$

Last-Modified

$Date$

Author

Benoit Bryon <benoit at marmelune.net>

Discussions-To

<distutils-sig at python.org>

Status

Deferred

Type

Informational

Content-Type

text/x-rst

Created

24-May-2012

Post-History

Contents

• Abstract

• PEP Deferral

• Terminology

• Relationship with other PEPs

• Overview

• If in doubt, ask

• Top-level namespace relates to code ownership

  • Respect ownership

  • Private (including closed-source) projects use a namespace

  • Individual projects use a namespace

  • Community-owned projects can avoid namespace packages

  • In doubt, use an individual/organization namespace

• Use a single name

  • Multiple packages/modules should be rare

  • Distinct names should be rare

• Follow PEP 8 for syntax of package and module names

• Pick memorable names

• Pick meaningful names

• Use packaging metadata

• Avoid deep nesting

  • Two levels is almost always enough

  • Use only one level for ownership

  • Don’t use namespace levels for categorization

  • Don’t use more than 3 levels

• Conventions for communities or related projects

  • Follow community or related project conventions, if any

  • Use standard pattern for community contributions

  • Organize community contributions

• Register names with PyPI

• Recipes

  • How to check for name availability?

  • How to rename a project?

    • Improved handling of renamed projects on PyPI

  • How to apply naming guidelines on existing projects?

    • State about current naming

    • Promote migrations

    • Opportunity

• References

• Copyright

Abstract

This document deals with:

• names of Python projects,

• names of Python packages or modules being distributed,

• namespace packages.

It provides guidelines and recipes for distribution authors:

• new projects should follow the guidelines below.

• existing projects should be aware of these guidelines and can follow specific recipes for existing projects.

PEP Deferral

Further consideration of this PEP has been deferred at least until after PEP 426 (package metadata 2.0) and related updates have been resolved.

Terminology

Reference is packaging terminology in Python documentation.

Relationship with other PEPs

• PEP 8 deals with code style guide, including names of Python packages and modules. It covers syntax of package/modules names.

• PEP 345 deals with packaging metadata, and defines name argument of the packaging.core.setup() function.

• PEP 420 deals with namespace packages. It brings support of namespace packages to Python core. Before, namespaces packages were implemented by external libraries.

• PEP 3108 deals with transition between Python 2.x and Python 3.x applied to standard library: some modules to be deleted, some to be renamed. It points out that naming conventions matter and is an example of transition plan.

Overview

Here is a summarized list of guidelines you should follow to choose names:

• understand and respect namespace ownership.

• if your project is related to another project or community:

  • search for conventions in main project’s documentation, because projects should organize community contributions.

  • follow specific project or related community conventions, if any.

  • if there is no convention, follow a standard naming pattern.

• make sure your project name is unique, i.e. avoid duplicates:

  • use top-level namespace for ownership,

  • check for name availability,

  • register names with PyPI.

• make sure distributed packages and modules names are unique, unless you explicitly want to distribute alternatives to existing packages or modules. Using the same value for package/module name and project name is the recommended way to achieve this.

• distribute only one package or module at a time, unless you know what you are doing. It makes it possible to apply the “use a single name” rule, and thus make names consistent.

• make it easy to discover and remember your project:

  • use as much memorable names as possible,

  • use as much meaningful names as possible,

  • use other packaging metadata.

• avoid deep nesting. Flat things are easier to use and remember than nested ones:

  • one or two namespace levels are recommended, because they are almost always enough.

  • even if not recommended, three levels are, de facto, a common case.

  • in most cases, you should not need more than three levels.

• follow PEP 8 for syntax of package and module names.

• if you followed specific conventions, or if your project is intended to receive contributions from the community, organize community contributions.

• if still in doubt, ask.

If in doubt, ask

If you feel unsure after reading this document, ask Python community on IRC or on a mailing list.

Top-level namespace relates to code ownership

This helps avoid clashes between project names.

Ownership could be:

• an individual. Example: gp.fileupload is owned and maintained by Gael Pasgrimaud.

• an organization. Examples:

  • zest.releaser is owned and maintained by Zest Software.

  • Django is owned and maintained by the Django Software Foundation.

• a group or community. Example: sphinx is maintained by developers of the Sphinx project, not only by its author, Georg Brandl.

• a group or community related to another package. Example: collective.recaptcha is owned by its author: David Glick, Groundwire. But the “collective” namespace is owned by Plone community.

Respect ownership

Understand the purpose of namespace before you use it.

Don’t plug into a namespace you don’t own, unless explicitly authorized.

If in doubt, ask.

As an example, don’t plug in “django.contrib” namespace because it is managed by Django’s core contributors.

Exceptions can be defined by project authors. See Organize community contributions below.

Also, this rule applies to non-Python projects.

As an example, don’t use “apache” as top-level namespace: “Apache” is the name of an existing project (in the case of “Apache”, it is also a trademark).

Private (including closed-source) projects use a namespace

… because private projects are owned by somebody. So apply the ownership rule.

For internal/customer projects, use your company name as the namespace.

This rule applies to closed-source projects.

As an example, if you are creating a “climbing” project for the “Python Sport” company: use “pythonsport.climbing” name, even if it is closed source.

Individual projects use a namespace

… because they are owned by individuals. So apply the ownership rule.

There is no shame in releasing a project as open source even if it has an “internal” or “individual” name.

If the project comes to a point where the author wants to change ownership (i.e. the project no longer belongs to an individual), keep in mind it is easy to rename the project.

Community-owned projects can avoid namespace packages

If your project is generic enough (i.e. it is not a contrib to another product or framework), you can avoid namespace packages. The base condition is generally that your project is owned by a group (i.e. the development team) which is dedicated to this project.

Only use a “shared” namespace if you really intend the code to be community owned.

As an example, sphinx project belongs to the Sphinx development team. There is no need to have some “sphinx” namespace package with only one “sphinx.sphinx” project inside.

In doubt, use an individual/organization namespace

If your project is really experimental, best choice is to use an individual or organization namespace:

• it allows projects to be released early.

• it won’t block a name if the project is abandoned.

• it doesn’t block future changes. When a project becomes mature and there is no reason to keep individual ownership, it remains possible to rename the project.

Use a single name

Distribute only one package (or only one module) per project, and use package (or module) name as project name.

• It avoids possible confusion between project name and distributed package or module name.

• It makes the name consistent.

• It is explicit: when one sees project name, he guesses package/module name, and vice versa.

• It also limits implicit clashes between package/module names. By using a single name, when you register a project name to PyPI, you also perform a basic package/module name availability verification.

  As an example, pipeline, python-pipeline and django-pipeline all distribute a package or module called “pipeline”. So installing two of them leads to errors. This issue wouldn’t have occurred if these distributions used a single name.

Yes:

• Package name: “kheops.pyramid”, i.e. import kheops.pyramid

• Project name: “kheops.pyramid”, i.e. pip install kheops.pyramid

No:

• Package name: “kheops”

• Project name: “KheopsPyramid”

Note

For historical reasons, PyPI contains many distributions where project and distributed package/module names differ.

Multiple packages/modules should be rare

Technically, Python distributions can provide multiple packages and/or modules. See setup script reference for details.

Some distributions actually do. As an example, setuptools and distribute are both declaring “pkg_resources”, “easy_install” and “site” modules in addition to respective “setuptools” and “distribute” packages.

Consider this use case as exceptional. In most cases, you don’t need this feature. So a distribution should provide only one package or module at a time.

Distinct names should be rare

A notable exception to the Use a single name rule is when you explicitly need distinct names.

As an example, the Pillow project provides an alternative to the original PIL distribution. Both projects distribute a “PIL” package.

Consider this use case as exceptional. In most cases, you don’t need this feature. So a distributed package name should be equal to project name.

Follow PEP 8 for syntax of package and module names

PEP 8 applies to names of Python packages and modules.

If you Use a single name, PEP 8 also applies to project names. The exceptions are namespace packages, where dots are required in project name.

Pick memorable names

One important thing about a project name is that it be memorable.

As an example, celery is not a meaningful name. At first, it is not obvious that it deals with message queuing. But it is memorable, partly because it can be used to feed a RabbitMQ server.

Pick meaningful names

Ask yourself “how would I describe in one sentence what this name is for?”, and then “could anyone have guessed that by looking at the name?”.

As an example, DateUtils is a meaningful name. It is obvious that it deals with utilities for dates.

When you are using namespaces, try to make each part meaningful.

Use packaging metadata

Consider project names as unique identifiers on PyPI:

• it is important that these identifiers remain human-readable.

• it is even better when these identifiers are meaningful.

• but the primary purpose of identifiers is not to classify or describe projects.

Classifiers and keywords metadata are made for categorization of distributions. Summary and description metadata are meant to describe the project.

As an example, there is a “Framework :: Twisted” classifier. Even if names are quite heterogeneous (they don’t follow a particular pattern), we get the list.

In order to Organize community contributions, conventions about names and namespaces matter, but conventions about metadata should be even more important.

As an example, we can find Plone portlets in many places:

• plone.portlet.*

• collective.portlet.*

• collective.portlets.*

• collective.*.portlets

• some vendor-related projects such as “quintagroup.portlet.cumulus”

• and even projects where “portlet” pattern doesn’t appear in the name.

Even if Plone community has conventions, using the name to categorize distributions is inappropriate. It’s impossible to get the full list of distributions that provide portlets for Plone by filtering on names. But it would be possible if all these distributions used “Framework :: Plone” classifier and “portlet” keyword.

Avoid deep nesting

The Zen of Python says “Flat is better than nested”.

Two levels is almost always enough

Don’t define everything in deeply nested hierarchies: you will end up with projects and packages like “pythonsport.common.maps.forest”. This type of name is both verbose and cumbersome (e.g. if you have many imports from the package).

Furthermore, big hierarchies tend to break down over time as the boundaries between different packages blur.

The consensus is that two levels of nesting are preferred.

For example, we have plone.principalsource instead of plone.source.principal or something like that. The name is shorter, the package structure is simpler, and there would be very little to gain from having three levels of nesting here. It would be impractical to try to put all “core Plone” sources (a source is kind of vocabulary) into the plone.source.* namespace, in part because some sources are part of other packages, and in part because sources already exist in other places. Had we made a new namespace, it would be inconsistently used from the start.

Yes: “pyranha”

Yes: “pythonsport.climbing”

Yes: “pythonsport.forestmap”

No: “pythonsport.maps.forest”

Use only one level for ownership

Don’t use 3 levels to set individual/organization ownership in a community namespace.

As an example, let’s consider:

• you are plugging into a community namespace, such as “collective”.

• and you want to add a more restrictive “ownership” level, to avoid clashes inside the community.

In such a case, you’d better use the most restrictive ownership level as first level.

As an example, where “collective” is a major community namespace that “gergovie” belongs to, and “vercingetorix” it the name of “gergovie” author:

No: “collective.vercingetorix.gergovie”

Yes: “vercingetorix.gergovie”

Don’t use namespace levels for categorization

Use packaging metadata instead.

Don’t use more than 3 levels

Technically, you can create deeply nested hierarchies. However, in most cases, you shouldn’t need it.

Note

Even communities where namespaces are standard don’t use more than 3 levels.

Conventions for communities or related projects

Follow community or related project conventions, if any

Projects or related communities can have specific conventions, which may differ from those explained in this document.

In such a case, they should declare specific conventions in documentation.

So, if your project belongs to another project or to a community, first look for specific conventions in main project’s documentation.

If there is no specific conventions, follow the ones declared in this document.

As an example, Plone community releases community contributions in the “collective” namespace package. It differs from the standard namespace for contributions proposed here. But since it is documented, there is no ambiguity and you should follow this specific convention.

Use standard pattern for community contributions

When no specific rule is defined, use the ${MAINPROJECT}contrib.${PROJECT} pattern to store community contributions for any product or framework, where:

• ${MAINPROJECT} is the name of the related project. “pyranha” in the example below.

• ${PROJECT} is the name of your project. “giantteeth” in the example below.

As an example:

• you are the author of “pyranha” project. You own the “pyranha” namespace.

• you didn’t defined specific naming conventions for community contributions.

• a third-party developer wants to publish a “giantteeth” project related to your “pyranha” project in a community namespace. So he should publish it as “pyranhacontrib.giantteeth”.

It is the simplest way to Organize community contributions.

Note

Why ${MAINPROJECT}contrib.* pattern?

• ${MAINPROJECT}c.* is not explicit enough. As examples, “zc” belongs to “Zope Corporation” whereas “z3c” belongs to “Zope 3 community”.

• ${MAINPROJECT}community is too long.

• ${MAINPROJECT}community conflicts with existing namespaces such as “iccommunity” or “PyCommunity”.

• ${MAINPROJECT}.contrib.* is inside ${MAINPROJECT} namespace, i.e. it is owned by ${MAINPROJECT} authors. It breaks the Top-level namespace relates to code ownership rule.

• ${MAINPROJECT}.contrib.* breaks the Avoid deep nesting rule.

• names where ${MAINPROJECT} doesn’t appear are not explicit enough, i.e. nobody can guess they are related to ${MAINPROJECT}. As an example, it is not obvious that “collective.*” belongs to Plone community.

• {$DIST}contrib.* looks like existing sphinxcontrib-* packages. But sphinxcontrib-* is actually about Sphinx contrib, so this is not a real conflict… In fact, the “contrib” suffix was inspired by “sphinxcontrib”.

Organize community contributions

This is the counterpart of the follow community conventions and standard pattern for contributions rules.

Actions:

• Choose a naming convention for community contributions.

• If it is not the default, then document it.

  • if you use the default convention, then this document should be enough. Don’t reapeat it. You may reference it.

  • else, tell users about custom conventions in project’s “contribute” or “create modules” documentation.

• Also recommend the use of additional metadata, such as classifiers and keywords.

About convention choices:

• New projects should choose the default contrib pattern.

• Existing projects with community contributions should start with custom conventions. Then they can Promote migrations.

  It means that existing community conventions don’t have to be changed. But, at least, they should be explicitly documented.

Example: “pyranha” is your project name and package name. Tell contributors that:

• pyranha-related distributions should use the “pyranha” keyword

• pyranha-related distributions providing templates should also use “templates” keyword.

• community contributions should be released under “pyranhacontrib” namespace (i.e. use “pyranhacontrib.*” pattern).

Register names with PyPI

PyPI is the central place for distributions in Python community. So, it is also the place where to register project and package names.

See Registering with the Package Index for details.

Recipes

The following recipes will help you follow the guidelines and conventions above.

How to check for name availability?

Before you choose a project name, make sure it hasn’t already been registered in the following locations:

• PyPI

• that’s all. PyPI is the only official place.

As an example, you could also check in various locations such as popular code hosting services, but keep in mind that PyPI is the only place you can register for names in Python community.

That’s why it is important you register names with PyPI.

Also make sure the names of distributed packages or modules haven’t already been registered:

• in the Python Standard Library.

• inside projects at PyPI. There is currently no helper for that. Notice that the more projects follow the use a single name rule, the easier is the verification.

• you may ask the community.

The use a single name rule also helps you avoid clashes with package names: if a project name is available, then the package name has good chances to be available too.

How to rename a project?

Renaming a project is possible, but keep in mind that it will cause some confusions. So, pay particular attention to README and documentation, so that users understand what happened.

1. First of all, do not remove legacy distributions from PyPI. Because some users may be using them.

2. Copy the legacy project, then change names (project and package/module). Pay attention to, at least:

   • packaging files,

   • folder name that contains source files,

   • documentation, including README,

   • import statements in code.

3. Assign Obsoletes-Dist metadata to new distribution in setup.cfg file. See PEP 345 about Obsolete-Dist and setup.cfg specification.

4. Release a new version of the renamed project, then publish it.

5. Edit legacy project:

   • add dependency to new project,

   • drop everything except packaging stuff,

   • add the Development Status :: 7 - Inactive classifier in setup script,

   • publish a new release.

So, users of the legacy package:

• can continue using the legacy distributions at a deprecated version,

• can upgrade to last version of legacy distribution, which is empty…

• … and automatically download new distribution as a dependency of the legacy one.

Users who discover the legacy project see it is inactive.

Improved handling of renamed projects on PyPI

If many projects follow Renaming howto recipe, then many legacy distributions will have the following characteristics:

• Development Status :: 7 - Inactive classifier.

• latest version is empty, except packaging stuff.

• latest version “redirects” to another distribution. E.g. it has a single dependency on the renamed project.

• referenced as Obsoletes-Dist in a newer distribution.

So it will be possible to detect renamed projects and improve readability on PyPI. So that users can focus on active distributions. But this feature is not required now. There is no urge. It won’t be covered in this document.

How to apply naming guidelines on existing projects?

There is no obligation for existing projects to be renamed. The choice is left to project authors and mainteners for obvious reasons.

However, project authors are invited to:

• at least, state about current naming.

• then plan and promote migration.

• optionally actually rename existing project or distributed packages/modules.

State about current naming

The important thing, at first, is that you state about current choices:

• Ask yourself “why did I choose the current name?”, then document it.

• If there are differences with the guidelines provided in this document, you should tell your users.

• If possible, create issues in the project’s bugtracker, at least for record. Then you are free to resolve them later, or maybe mark them as “wontfix”.

Projects that are meant to receive contributions from community should also organize community contributions.

Promote migrations

Every Python developer should migrate whenever possible, or promote the migrations in their respective communities.

Apply these guidelines on your projects, then the community will see it is safe.

In particular, “leaders” such as authors of popular projects are influential, they have power and, thus, responsibility over communities.

Apply these guidelines on popular projects, then communities will adopt the conventions too.

Projects should promote migrations when they release a new (major) version, particularly if this version introduces support for Python 3.x, new standard library’s packaging or namespace packages.

Opportunity

As of Python 3.3 being developed:

• many projects are not Python 3.x compatible. It includes “big” products or frameworks. It means that many projects will have to do a migration to support Python 3.x.

• packaging (aka distutils2) is on the starting blocks. When it is released, projects will be invited to migrate and use new packaging.

• PEP 420 brings official support of namespace packages to Python.

It means that most active projects should be about to migrate in the next year(s) to support Python 3.x, new packaging or new namespace packages.

Such an opportunity is unique and won’t come again soon! So let’s introduce and promote naming conventions as soon as possible (i.e. now).

References

Additional background:

• Martin Aspeli’s article about names. Some parts of this document are quotes from this article.

• in development official packaging documentation.

• The Hitchhiker’s Guide to Packaging, which has an empty placeholder for “naming specification”.

References and footnotes:

Copyright

This document has been placed in the public domain.