Recording installed projects#

This document specifies a common format of recording information about Python projects 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.

The .dist-info directory#

Each project installed from a distribution must, 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 Core metadata specifications. Both fields must be normalized (see the name normalization specification and the version normalization specification), and replace dash (-) characters with underscore (_) characters, so the .dist-info directory always has exactly one dash (-) character in its stem, separating the name and version fields.

Historically, tools have failed to replace dot characters or normalize case in the name field, or not perform normalization in the version field. Tools consuming .dist-info directories should expect those fields to be unnormalized, and treat them as equivalent to their normalized counterparts. New tools that write .dist-info directories MUST normalize both name and version fields using the rules described above, and existing tools are encouraged to start normalizing those fields.

Note

The .dist-info directory’s name is formatted to unambiguously represent a distribution as a filesystem path. Tools presenting a distribution name to a user should avoid using the normalized name, and instead present the specified name (when needed prior to resolution to an installed package), or read the respective fields in Core Metadata, since values listed there are unescaped and accurately reflect the distribution. Libraries should provide API for such tools to consume, so tools can have access to the unnormalized name when displaying distribution information.

This .dist-info directory may contain the following files, described in detail below:

The METADATA file is mandatory. All other files may be omitted at the installing tool’s discretion. Additional installer-specific files may be present.

Note

The Binary distribution format specification describes additional files that may appear in the .dist-info directory of a Wheel. Such files may be copied to the .dist-info directory of an installed project.

The previous versions of this specification also specified a REQUESTED file. This file is now considered a tool-specific extension, but may be standardized again in the future. See PEP 376 for its original meaning.

The METADATA file#

The METADATA file contains metadata as described in the Core metadata specifications specification, version 1.1 or greater.

The METADATA file is mandatory. If it cannot be created, or if required core metadata is not available, installers must report an error and fail to install the project.

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 discouraged, 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

If the RECORD file is missing, tools that rely on .dist-info must not attempt to uninstall or upgrade the package. (This restriction does not apply to tools that rely on other sources of information, such as system package managers in Linux distros.)

Note

It is strongly discouraged for an installed package to modify itself (e.g., store cache files under its namespace in site-packages). Changes inside site-packages should be left to specialized installer tools such as pip. If a package is nevertheless modified in this way, then the RECORD must be updated, otherwise uninstalling the package will leave unlisted files in place (possibly resulting in a zombie namespace package).

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

MegaCorp Cloud Install-O-Matic

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.

The entry_points.txt file#

This file MAY be created by installers to indicate when packages contain components intended for discovery and use by other code, including console scripts and other applications that the installer has made available for execution.

Its detailed specification is at Entry points specification.

The direct_url.json file#

This file MUST be created by installers when installing a distribution from a requirement specifying a direct URL reference (including a VCS URL).

This file MUST NOT be created when installing a distribution from an other type of requirement (i.e. name plus version specifier).

Its detailed specification is at Recording the Direct URL Origin of installed distributions.

Intentionally preventing changes to installed packages#

In some cases (such as when needing to manage external dependencies in addition to Python ecosystem dependencies), it is desirable for a tool that installs packages into a Python environment to ensure that other tools are not used to uninstall or otherwise modify that installed package, as doing so may cause compatibility problems with the wider environment.

To achieve this, affected tools should take the following steps:

  • Rename or remove the RECORD file to prevent changes via other tools (e.g. appending a suffix to create a non-standard RECORD.tool file if the tool itself needs the information, or omitting the file entirely if the package contents are tracked and managed via other means)

  • Write an INSTALLER file indicating the name of the tool that should be used to manage the package (this allows RECORD-aware tools to provide better error notices when asked to modify affected packages)

Python runtime providers may also prevent inadvertent modification of platform provided packages by modifying the default Python package installation scheme to use a location other than that used by platform provided packages (while also ensuring both locations appear on the default Python import path).

In some circumstances, it may be desirable to block even installation of additional packages via Python-specific tools. For these cases refer to Externally Managed Environments

History#

  • June 2009: The original version of this specification was approved through PEP 376. At the time, it was known as the Database of Installed Python Distributions.

  • March 2020: The specification of the direct_url.json file was approved through PEP 610. It is only mentioned on this page; see Recording the Direct URL Origin of installed distributions for the full definition.

  • September 2020: Various amendments and clarifications were approved through PEP 627.