PEP 627: Recording installed projects

Author: encukou

source/specifications/distribution-formats.rst

@@ -17,6 +17,8 @@ There is also the legacy source distribution format, implicitly defined by
 the behaviour of ``distutils`` module in the standard library,
 when executing ``setup.py sdist``.
 
+.. _binary-distribution-format:
+
 Binary distribution format
 ==========================
 

source/specifications/recording-installed-packages.rst

@@ -1,12 +1,161 @@
-
 .. _recording-installed-packages:
 
-=================================
-Recording installed distributions
-=================================
+============================
+Recording installed projects
+============================
+
+This document specifies a common format of recording information
+about Python :term:`projects <project>` installed in an environment.
+A common metadata format allows tools to query, manage or uninstall projects,
+regardless of how they were installed.
+
+Almost all information is optional.
+This allows tools outside the Python ecosystem, such as Linux package managers,
+to integrate with Python tooling as much as possible.
+For example, even if an installer cannot easily provide a list of installed
+files in a format specific to Python tooling, it should still record the name
+and version of the installed project.
+
+
+History and change workflow
+===========================
+
+The metadata described here was first specified in :pep:`376`, and later
+ammended in :pep:`627`.
+It was formerly known as *Database of Installed Python Distributions*.
+Further amendments (except trivial language or typography fixes) must be made
+through the PEP process (see :pep:`1`).
+
+While this document is the normative specification, these PEPs that introduce
+changes to it may include additional information such as rationales and
+backwards compatibility considerations.
+
+
+The .dist-info directory
+========================
+
+Each project installed from a distribution shall, in addition to files,
+install a "``.dist-info``" directory located alongside Importable modules and
+packages (commonly, the ``site-packages`` directory).
+
+This directory is named as ``{name}-{version}.dist-info``, with `name` and
+`version` fields corresponding to :ref:`core-metadata`.
+
+This ``.dist-info`` directory can contain these files, described in detail
+below:
+
+* ``METADATA``: contains project metadata
+* ``RECORD``: records the list of installed files.
+* ``INSTALLER``: records the name of the tool used to install the project.
+
+Only the ``METADATA`` file is mandatory.
+Additional installer-specific files may be present.
+
+.. note::
+
+   The :ref:`binary-distribution-format` specification describes additional
+   files that may appear in the ``.dist-info`` directory of a :term:`wheel`.
+   Such files may be copied to the ``.dist-info`` directory of an
+installed project.
+
+
+The METADATA file
+=================
+
+The ``METADATA`` file contains metadata as described in the :ref:`core-metadata`
+specification, version 1.1 or greater.
+
+The ``METADATA`` file is mandatory.
+If it cannot be created, or if required core metadata is not available,
+no ``.dist-info`` directory should be created at all.
+
+
+The RECORD file
+===============
+
+The ``RECORD`` file holds the list of installed files.
+It is a CSV file containing one record (line) per installed file.
+
+The CSV dialect must be readable with the default `reader` of Python's `csv` module:
+
+* field delimiter: ``,`` (comma),
+* quoting char: ``"`` (straight double quote),
+* line terminator: either ``\r\n`` or ``\n``.
+
+Each record is composed of three elements: the file's **path**, the **hash**
+of the contents, and its **size**.
+
+The *path* may be either absolute, or relative to the directory containing
+the ``.dist-info`` directory (commonly, the ``site-packages`` directory).
+On Windows, directories may be separated either by forward- or backslashes
+(``/`` or ``\``).
+
+The *hash* is either an empty string or the name of a hash algorithm from
+``hashlib.algorithms_guaranteed``, followed by the equals character ``=`` and
+the digest of the file's contents, encoded with the urlsafe-base64-nopad
+encoding (``base64.urlsafe_b64encode(digest)`` with trailing ``=`` removed).
+
+The *size* is either the empty string, or file's size in bytes,
+as a base 10 integer.
+
+For any file, either or both of the *hash* and *size* fields may be left empty.
+Commonly, entries for ``.pyc`` files and the ``RECORD`` file itself have empty
+*hash* and *size*.
+For other files, leaving the information out is not recommended, as it
+prevents verifying the integrity of the installed project.
+
+If the ``RECORD`` file is present, it must list all installed files of the
+project, except `.pyc` files corresponding to `.py` files listed in
+``RECORD``, which are optional.
+Notably, the contents of the ``.dist-info`` directory (including the ``RECORD``
+file itself) must be listed.
+Directories should not be listed.
+
+To completely uninstall a package, a tool needs to remove all
+files listed in ``RECORD``, all ``.pyc`` files (of all optimization levels)
+corresponding to removed ``.py`` files, and any directories emptied by
+the uninstallation.
+
+Here is an example snippet of a possible ``RECORD`` file::
+
+    /usr/bin/black,sha256=iFlOnL32lIa-RKk-MDihcbJ37wxmRbE4xk6eVYVTTeU,220
+    ../../../bin/blackd,sha256=lCadt4mcU-B67O1gkQVh7-vsKgLpx6ny1le34Jz6UVo,221
+    __pycache__/black.cpython-38.pyc,,
+    __pycache__/blackd.cpython-38.pyc,,
+    black-19.10b0.dist-info/INSTALLER,sha256=zuuue4knoyJ-UwPPXg8fezS7VCrXJQrAP7zeNuwvFQg,4
+    black-19.10b0.dist-info/LICENSE,sha256=nAQo8MO0d5hQz1vZbhGqqK_HLUqG1KNiI9erouWNbgA,1080
+    black-19.10b0.dist-info/METADATA,sha256=UN40nGoVVTSpvLrTBwNsXgZdZIwoKFSrrDDHP6B7-A0,58841
+    black-19.10b0.dist-info/RECORD,,
+    black.py,sha256=45IF72OgNfF8WpeNHnxV2QGfbCLubV5Xjl55cI65kYs,140161
+    blackd.py,sha256=JCxaK4hLkMRwVfZMj8FRpRRYC0172-juKqbN22bISLE,6672
+    blib2to3/__init__.py,sha256=9_8wL9Scv8_Cs8HJyJHGvx1vwXErsuvlsAqNZLcJQR0,8
+    blib2to3/__pycache__/__init__.cpython-38.pyc,,
+    blib2to3/__pycache__/pygram.cpython-38.pyc,sha256=zpXgX4FHDuoeIQKO_v0sRsB-RzQFsuoKoBYvraAdoJw,1512
+    blib2to3/__pycache__/pytree.cpython-38.pyc,sha256=LYLplXtG578ZjaFeoVuoX8rmxHn-BMAamCOsJMU1b9I,24910
+    blib2to3/pygram.py,sha256=mXpQPqHcamFwch0RkyJsb92Wd0kUP3TW7d-u9dWhCGY,2085
+    blib2to3/pytree.py,sha256=RWj3IL4U-Ljhkn4laN0C3p7IRdfvT3aIRjTV-x9hK1c,28530
+
+
+The INSTALLER file
+==================
+
+If present, ``INSTALLER`` is a single-line text file naming the tool used to
+install the project.
+If the installer is executable from the command line, ``INSTALLER``
+should contain the command name.
+Otherwise, it should contain a printable ASCII string.
+
+The file can be terminated by zero or more ASCII whitespace characters.
+
+Here are examples of two possible ``INSTALLER`` files::
+
+    pip
+
+::
 
-The format used to record installed packages and their contents is defined in
-:pep:`376`.
+    MegaCorp Cloud Install-O-Matic
 
-Note that only the ``dist-info`` directory and the ``RECORD`` file format from
-that PEP are currently implemented in the default packaging toolchain.
+This value should be used for informational purposes only.
+For example, if a tool is asked to uninstall a project but finds no ``RECORD``
+file, it may suggest that the tool named in ``INSTALLER`` may be able to do the
+uninstallation.