License

A short string summarising the license used for this distribution.

Note that distributions that provide this field should still specify any applicable license Trove classifiers in the Classifiers field. Even when an appropriate Trove classifier is available, the license summary can be a good way to specify a particular version of that license, or to indicate any variations or exception to the license.

This field SHOULD contain fewer than 512 characters and MUST contain fewer than 2048.

This field SHOULD NOT contain any line breaks.

The full license text SHOULD be included as a separate file in the source archive for the distribution. See Document names for details.

Example:

"license": "GPL version 3, excluding DRM provisions"

Keywords

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

Example:

"keywords": ["comfy", "chair", "cushions", "too silly", "monty python"]

Classifiers

A list of strings, with each giving a single classification value for the distribution. Classifiers are described in PEP 301 [2].

Example:

"classifiers": [
  "Development Status :: 4 - Beta",
  "Environment :: Console (Text Based)",
  "License :: OSI Approved :: GNU General Public License v3 (GPLv3)"
]

Document names

Filenames for supporting documents included in the distribution’s dist-info metadata directory.

The following supporting documents can be named:

• description: a file containing a long description of the distribution
• license: a file with the full text of the distribution’s license
• changelog: a file describing changes made to the distribution

Supporting documents MUST be included directly in the dist-info directory. Directory separators are NOT permitted in document names.

The markup format (if any) for the file is indicated by the file extension. This allows index servers and other automated tools to render included text documents correctly and provide feedback on rendering errors, rather than having to guess the intended format.

If the filename has no extension, or the extension is not recognised, the default rendering format MUST be plain text.

The following markup renderers SHOULD be used for the specified file extensions:

• Plain text: .txt, no extension, unknown extension
• reStructured Text: .rst
• Markdown: .md
• AsciiDoc: .adoc, .asc, .asciidoc
• HTML: .html, .htm

Automated tools MAY render one or more of the specified formats as plain text and MAY render other markup formats beyond those listed.

Automated tools SHOULD NOT make any assumptions regarding the maximum length of supporting document content, except as necessary to protect the integrity of a service.

Example:

"document_names": {
    "description": "README.rst",
    "license": "LICENSE.rst",
    "changelog": "NEWS"
}

Contact information

Details on individuals and organisations are recorded as mappings with the following subfields:

• name: the name of an individual or group
• email: an email address (this may be a mailing list)
• url: a URL (such as a profile page on a source code hosting service)
• role: one of "author", "maintainer" or "contributor"

The name subfield is required, the other subfields are optional.

If no specific role is stated, the default is contributor.

Email addresses must be in the form local-part@domain where the local-part may be up to 64 characters long and the entire email address contains no more than 254 characters. The formal specification of the format is in RFC 5322 (sections 3.2.3 and 3.4.1) and RFC 5321, with a more readable form given in the informational RFC 3696 and the associated errata.

The defined contributor roles are as follows:

• author: the original creator of a distribution
• maintainer: the current lead contributor for a distribution, when they are not the original creator
• contributor: any other individuals or organizations involved in the creation of the distribution

Contact and contributor metadata is optional. Automated tools MUST operate correctly if a distribution does not provide it, including failing cleanly when an operation depending on one of these fields is requested.

Contacts

A list of contributor entries giving the recommended contact points for getting more information about the project.

The example below would be suitable for a project that was in the process of handing over from the original author to a new lead maintainer, while operating as part of a larger development group.

Example:

"contacts": [
  {
    "name": "Python Packaging Authority/Distutils-SIG",
    "email": "distutils-sig@python.org",
    "url": "https://bitbucket.org/pypa/"
  },
  {
    "name": "Samantha C.",
    "role": "maintainer",
    "email": "dontblameme@example.org"
  },
  {
    "name": "Charlotte C.",
    "role": "author",
    "email": "iambecomingasketchcomedian@example.com"
  }
]

Contributors

A list of contributor entries for other contributors not already listed as current project points of contact. The subfields within the list elements are the same as those for the main contact field.

Example:

"contributors": [
  {"name": "John C."},
  {"name": "Erik I."},
  {"name": "Terry G."},
  {"name": "Mike P."},
  {"name": "Graeme C."},
  {"name": "Terry J."}
]

Project URLs

A mapping of arbitrary text labels to additional URLs relevant to the project.

While projects are free to choose their own labels and specific URLs, it is RECOMMENDED that home page, source control, issue tracker and documentation links be provided using the labels in the example below.

URL labels MUST be treated as case insensitive by automated tools, but they are not required to be valid Python identifiers. Any legal JSON string is permitted as a URL label.

Example:

"project_urls": {
  "Documentation": "https://distlib.readthedocs.org",
  "Home": "https://bitbucket.org/pypa/distlib",
  "Repository": "https://bitbucket.org/pypa/distlib/src",
  "Tracker": "https://bitbucket.org/pypa/distlib/issues"
}

Export specifiers

An export specifier is a string consisting of a fully qualified name, as well as an optional extra name enclosed in square brackets. This gives the following four possible forms for an export specifier:

module
module:name
module[requires_extra]
module:name[requires_extra]

The meaning of the subfields is as follows:

• module: the module providing the export
• name: if applicable, the qualified name of the export within the module
• requires_extra: indicates the export will only work correctly if the additional dependencies named in the given extra are available in the installed environment

Modules

A list of qualified names of modules and packages that the distribution provides for import.

For names that contain dots, the portion of the name before the final dot MUST appear either in the installed module list or in the namespace package list.

To help avoid name conflicts, it is RECOMMENDED that distributions provide a single top level module or package that matches the distribution name (or a lower case equivalent). This requires that the distribution name also meet the requirements of a Python identifier, which are stricter than those for distribution names). This practice will also make it easier to find authoritative sources for modules.

Index servers SHOULD allow multiple distributions to publish the same modules, but MAY notify distribution authors of potential conflicts.

Installation tools SHOULD report an error when asked to install a distribution that provides a module that is also provided by a different, previously installed, distribution.

Note that attempting to import some declared modules may result in an exception if the appropriate extras are not installed.

Example:

"modules": ["chair", "chair.cushions", "python_sketches.nobody_expects"]

Namespaces

A list of qualified names of namespace packages that the distribution contributes modules to.

On versions of Python prior to Python 3.3 (which provides native namespace package support), installation tools SHOULD emit a suitable __init__.py file to properly initialise the namespace rather than using a distribution provided file.

Installation tools SHOULD emit a warning and MAY emit an error if a distribution declares a namespace package that conflicts with the name of an already installed module or vice-versa.

Example:

"namespaces": ["python_sketches"]

Exports

The exports field is a mapping containing prefixed names as keys. Each key identifies an export group containing one or more exports published by the distribution.

Export group names are defined by distributions that will then make use of the published export information in some way. The primary use case is for distributions that support a plugin model: defining an export group allows other distributions to indicate which plugins they provide, how they can be imported and accessed, and which additional dependencies (if any) are needed for the plugin to work correctly.

To reduce the chance of name conflicts, export group names SHOULD use a prefix that corresponds to a module name in the distribution that defines the meaning of the export group. This practice will also make it easier to find authoritative documentation for export groups.

Each individual export group is then a mapping of arbitrary non-empty string keys to export specifiers. The meaning of export names within an export group is up to the distribution that defines the export group. Creating an appropriate definition for the export name format can allow the importing distribution to determine whether or not an export is relevant without needing to import every exporting module.

Example:

"exports": {
  "nose.plugins.0.10": {
    "chairtest": "chair:NosePlugin"
  }
}

Supported Environments

The environments subfield is a list of strings specifying the environments that the distribution explicitly supports. An environment is considered supported if it matches at least one of the environment markers given.

If this field is not given in the metadata, it is assumed that the distribution supports any platform supported by Python.

Individual entries are environment markers, as described in PEP 426.

The two main uses of this field are to declare which versions of Python and which underlying operating systems are supported.

Examples indicating supported Python versions:

# Supports Python 2.6+
"environments": ["python_version >= '2.6'"]

# Supports Python 2.6+ (for 2.x) or 3.3+ (for 3.x)
"environments": ["python_version >= '3.3'",
                 "'3.0' > python_version >= '2.6'"]

Examples indicating supported operating systems:

# Windows only
"environments": ["sys_platform == 'win32'"]

# Anything except Windows
"environments": ["sys_platform != 'win32'"]

# Linux or BSD only
"environments": ["'linux' in sys_platform",
                 "'bsd' in sys_platform"]

Example where the supported Python version varies by platform:

# The standard library's os module has long supported atomic renaming
# on POSIX systems, but only gained atomic renaming on Windows in Python
# 3.3. A distribution that needs atomic renaming support for reliable
# operation might declare the following supported environments.
"environment": ["python_version >= '2.6' and sys_platform != 'win32'",
                "python_version >= '3.3' and sys_platform == 'win32'"]

Extension metadata constraints

The extension_metadata subfield is a mapping from distribution names to extension metadata snippets that are expected to exactly match the metadata of the named distribution in the target installation environment.

Each submapping then consists of a mapping from metadata extension names to the exact expected values of a subset of fields.

For example, a distribution called fortranlib may publish a different FORTRAN ABI depending on how it is built, and any related projects that are installed into the same runtime environment should use matching build options. This can be handled by having the base distribution publish a custom extension that indicates the build option that was used to create the binary extensions:

"extensions": {
  "fortranlib.compatibility": {
    "fortran_abi": "openblas-g77"
  }
}

Other distributions that contain binary extensions that need to be compatible with the base distribution would then define a suitable constraint in their own metadata:

"python.constraints": {
  "installer_must_handle": true,
  "extension_metadata": {
    "fortranlib": {
      "fortranlib.compatibility": {
        "fortran_abi": "openblas-g77"
      }
    }
  }
}

This constraint specifies that:

• fortranlib must be installed (this should also be expressed as a normal dependency so that installers ensure it is satisfied)
• The installed version of fortranlib must include the custom fortranlib.compatibility extension in its published metadata
• The fortan_abi subfield of that extension must have the exact value openblas-g77.

If all of these conditions are met (the distribution is installed, the specified extension is included in the metadata, the specified subfields have the exact specified value), then the constraint is considered to be satisfied.