Add PEP 794: Import name metadata

Author: brettcannon

source/specifications/core-metadata.rst

@@ -6,7 +6,7 @@
 Core metadata specifications
 ============================
 
-This page describes version 2.4, approved in August 2024.
+This page describes version 2.5, approved in September 2025.
 
 Fields defined in the following specification should be considered valid,
 complete and not subject to change. The required fields are:
@@ -50,7 +50,7 @@ Metadata-Version
 .. versionadded:: 1.0
 
 Version of the file format; legal values are "1.0", "1.1", "1.2", "2.1",
-"2.2", "2.3", and "2.4".
+"2.2", "2.3", "2.4", and "2.5".
 
 Automated tools consuming metadata SHOULD warn if ``metadata_version`` is
 greater than the highest version they support, and MUST fail if
@@ -718,6 +718,101 @@ user SHOULD be warned and the value ignored to avoid ambiguity. Tools MAY choose
 to raise an error when reading an invalid name for older metadata versions.
 
 
+.. _core-metadata-import-name:
+
+Import-Name (multiple use)
+===========================
+
+.. versionadded:: 2.5
+
+A string containing an import name that the project exclusively provides when
+installed. The specified import name MUST be a valid Python identifier or can
+be empty. The import names listed in this field MUST be importable when the
+project is installed on *some* platform for the same version of the project.
+This implies that the metadata MUST be consistent across all sdists and wheels
+for a project release.
+
+An import name MAY be followed by a semicolon and the term "private"
+(e.g. ``; private``) with any amount of whitespace surrounding the semicolon.
+This signals to tools that the import name is not part of the public API for
+the project.
+
+Projects SHOULD list all the shortest import names that are exclusively provided
+by the project. If any of the shortest names are dotted names, all intervening
+names from that name to the top-level name should also be listed appropriately
+in ``Import-Name`` and/or ``Import-Namespace``.
+
+If a project lists the same name in both ``Import-Name`` and
+``Import-Namespace``, tools MUST raise an error due to ambiguity.
+
+Tools SHOULD raise an error when two projects that are about to be installed
+list names that overlap in each other's ``Import-Name`` entries, or when a
+project has an entry in ``Import-Name`` that overlaps with another project's
+``Import-Namespace`` entries. This is to avoid projects unexpectedly shadowing
+another project's code. Tools MAY warn or raise an error when installing a
+project into a preexisting environment where there is import name overlap with
+a project that is already installed.
+
+Projects MAY have an empty ``Import-Name`` field in their metadata to represent
+a project with no import names (i.e. there are no Python modules of any kind in
+the distribution file).
+
+Since projects MAY have no ``Import-Name`` metadata (either because the
+project uses an older metadata version, or because it didn't specify any), then
+tools have no information about what names the project provides. However, in
+practice the majority of projects have their project name match what their
+import name would be. As such, it is a reasonable assumption to make that a
+project name that is normalized in some way to an import name
+(e.g. ``packaging.utils.canonicalize_name(name, validate=True).replace("-", "_")``)
+can be used if some answer is needed.
+
+Examples::
+
+    Import-Name: PIL
+    Import-Name: _private_module ; private
+    Import-Name: zope.interface
+    Import-Name:
+
+
+.. _core-metadata-import-namespace:
+
+Import-Namespace (multiple use)
+================================
+
+.. versionadded:: 2.5
+
+A string containing an import name that the project provides when installed, but
+not exclusively. The specified import name MUST be a valid Python identifier.
+This field is used for namespace packages where multiple projects can contribute
+to the same import namespace. Projects all listing the same import name in
+``Import-Namespace`` can be installed together without shadowing each other.
+
+An import name MAY be followed by a semicolon and the term "private" (e.g.
+``; private``) with any amount of whitespace surrounding the semicolon. This
+signals to tools that the import name is not part of the public API for the
+project.
+
+Projects SHOULD list all the shortest import names that are exclusively provided
+by the project. If any of the shortest names are dotted names, all intervening
+names from that name to the top-level name should also be listed appropriately
+in ``Import-Name`` and/or ``Import-Namespace``.
+
+The import names listed in this field MUST be importable when the project is
+installed on *some* platform for the same version of the project. This implies
+that the metadata MUST be consistent across all sdists and wheels for a project
+release.
+
+If a project lists the same name in both ``Import-Name`` and
+``Import-Namespace``, tools MUST raise an error due to ambiguity.
+
+Note that ``Import-Namespace`` CANNOT be empty like ``Import-Name``.
+
+Examples::
+
+    Import-Namespace: zope
+    Import-Name: _private_module ; private
+
+
 Rarely Used Fields
 ==================
 
@@ -933,34 +1028,39 @@ Example::
 History
 =======
 
-- August 2025: Clarified that ``Dynamic`` only affects how fields
-  must be treated when building a wheel from a sdist, not when modifying
-  a wheel.
+- March 2001: Core metadata 1.0 was approved through :pep:`241`.
 
-- August 2024: Core metadata 2.4 was approved through :pep:`639`.
+- April 2003: Core metadata 1.1 was approved through :pep:`314`.
 
-  - Added the ``License-Expression`` field.
-  - Added the ``License-File`` field.
+- February 2010: Core metadata 1.2 was approved through :pep:`345`.
 
-- March 2022: Core metadata 2.3 was approved through :pep:`685`.
+- February 2018: Core metadata 2.1 was approved through :pep:`566`.
 
-  - Restricted extra names to be normalized.
+  - Added ``Description-Content-Type`` and ``Provides-Extra``.
+  - Added canonical method for transforming metadata to JSON.
+  - Restricted the grammar of the ``Name`` field.
 
 - October 2020: Core metadata 2.2 was approved through :pep:`643`.
 
   - Added the ``Dynamic`` field.
 
-- February 2018: Core metadata 2.1 was approved through :pep:`566`.
+- March 2022: Core metadata 2.3 was approved through :pep:`685`.
 
-  - Added ``Description-Content-Type`` and ``Provides-Extra``.
-  - Added canonical method for transforming metadata to JSON.
-  - Restricted the grammar of the ``Name`` field.
+  - Restricted extra names to be normalized.
 
-- February 2010: Core metadata 1.2 was approved through :pep:`345`.
+- August 2024: Core metadata 2.4 was approved through :pep:`639`.
 
-- April 2003: Core metadata 1.1 was approved through :pep:`314`:
+  - Added the ``License-Expression`` field.
+  - Added the ``License-File`` field.
 
-- March 2001: Core metadata 1.0 was approved through :pep:`241`.
+- August 2025: Clarified that ``Dynamic`` only affects how fields
+  must be treated when building a wheel from a sdist, not when modifying
+  a wheel.
+
+- September 2025: Core metadata 2.5 was approved through :pep:`794`.
+
+  - Added the ``Import-Name`` field.
+  - Added the ``Import-Namespace`` field.
 
 ----
 

source/specifications/pyproject-toml.rst

@@ -136,6 +136,8 @@ The complete list of keys allowed in the ``[project]`` table are:
 - ``dynamic``
 - ``entry-points``
 - ``gui-scripts``
+- ``import-names``
+- ``import-namespaces``
 - ``keywords``
 - ``license``
 - ``license-files``
@@ -466,6 +468,97 @@ matching :ref:`Provides-Extra <core-metadata-provides-extra>`
 metadata.
 
 
+.. _pyproject-toml-import-names:
+
+``import-names``
+----------------
+
+- TOML_ type: array of strings
+- Corresponding :ref:`core metadata <core-metadata>` field:
+  :ref:`Import-Name <core-metadata-import-name>`
+
+An array of strings specifying the import names that the project exclusively
+provides when installed. Each string MUST be a valid Python identifier or can
+be empty. An import name MAY be followed by a semicolon and the term "private"
+(e.g. ``"; private"``) with any amount of whitespace surrounding the semicolon.
+
+Projects SHOULD list all the shortest import names that are exclusively provided
+by the project. If any of the shortest names are dotted names, all intervening
+names from that name to the top-level name should also be listed appropriately
+in ``import-names`` and/or ``import-namespaces``. For instance, a project which
+is a single package named spam with multiple submodules would only list
+``project.import-names = ["spam"]``. A project that lists ``spam.bacon.eggs``
+would also need to account for ``spam`` and ``spam.bacon`` appropriately in
+``import-names`` and ``import-namespaces``. Listing all names acts as a check
+that the intent of the import names is as expected. As well, projects SHOULD
+list all import names, public or private, using the ``; private`` modifier as
+appropriate.
+
+If a project lists the same name in both ``import-names`` and
+``import-namespaces``, then tools MUST raise an error due to ambiguity.
+
+Projects MAY set ``import-names`` to an empty array to represent a project with
+no import names (i.e. there are no Python modules of any kind in the
+distribution file).
+
+Build back-ends MAY support dynamically calculating the value if the user
+declares the key in ``project.dynamic``.
+
+Examples:
+
+.. code-block:: toml
+
+   [project]
+   name = "pillow"
+   import-names = ["PIL"]
+
+.. code-block:: toml
+
+   [project]
+   name = "myproject"
+   import-names = ["mypackage", "_private_module ; private"]
+
+
+.. _pyproject-toml-import-namespaces:
+
+``import-namespaces``
+---------------------
+
+- TOML_ type: array of strings
+- Corresponding :ref:`core metadata <core-metadata>` field:
+  :ref:`Import-Namespace <core-metadata-import-namespace>`
+
+An array of strings specifying the import names that the project provides when
+installed, but not exclusively. Each string MUST be a valid Python identifier.
+An import name MAY be followed by a semicolon and the term "private" (e.g.
+``"; private"``) with any amount of whitespace surrounding the semicolon. Note
+that unlike ``import-names``, ``import-namespaces`` CANNOT be an empty array.
+
+Projects SHOULD list all the shortest import names that are exclusively provided
+by the project. If any of the shortest names are dotted names, all intervening
+names from that name to the top-level name should also be listed appropriately
+in ``import-names`` and/or ``import-namespaces``.
+
+This field is used for namespace packages where multiple projects can contribute
+to the same import namespace. Projects all listing the same import name in
+``import-namespaces`` can be installed together without shadowing each other.
+
+If a project lists the same name in both ``import-names`` and
+``import-namespaces``, then tools MUST raise an error due to ambiguity.
+
+Build back-ends MAY support dynamically calculating the value if the user
+declares the key in ``project.dynamic``.
+
+Example:
+
+.. code-block:: toml
+
+   [project]
+   name = "zope-interface"
+   import-namespaces = ["zope"]
+   import-names = ["zope.interface"]
+
+
 .. _pyproject-toml-dynamic:
 .. _declaring-project-metadata-dynamic:
 
@@ -540,5 +633,8 @@ History
 - December 2024: The ``license`` key was redefined, the ``license-files`` key was
   added and ``License::`` classifiers were deprecated through :pep:`639`.
 
+- September 2025: The ``import-names`` and ``import-namespaces`` keys were added
+  through :pep:`794`.
+
 
 .. _TOML: https://toml.io