PEP 665 – A file format to list Python dependencies for reproducibility of an application
- A file format to list Python dependencies for reproducibility of an application
- Brett Cannon <brett at python.org>, Pradyun Gedam <pradyunsg at gmail.com>, Tzu-ping Chung <uranusjr at gmail.com>
- Paul Moore <p.f.moore at gmail.com>
- Standards Track
- 29-Jul-2021, 03-Nov-2021, 25-Nov-2021
- Expectations for Lockers
- Expectations for Installers
- (Potential) Tool Support
- Backwards Compatibility
- Transition Plan
- Security Implications
- How to Teach This
- Reference Implementation
- Rejected Ideas
- File Formats Other Than TOML
- Alternative Naming Schemes
- Supporting a Single Lock File
- Using a Flat List Instead of a Dependency Graph
- Use Wheel Tags in the File Name
- Alternative Names for
- Accepting PEP 650
- Specifying Requirements per Package Instead of per File
- Specify Where Lockers Gather Input
- Allowing Source Distributions and Source Trees to be an Opt-In, Supported File Format
- Open Issues
This PEP was rejected due to lukewarm reception from the community from the lack of source distribution support.
This PEP specifies a file format to specify the list of Python package installation requirements for an application, and the relation between the specified requirements. The list of requirements is considered exhaustive for the installation target, and thus not requiring any information beyond the platform being installed for, and the file itself. The file format is flexible enough to allow installing the requirements across different platforms, which allows for reproducibility on multiple platforms from the same file.
There are several terms whose definition must be agreed upon in order to facilitate a discussion on the topic of this PEP.
A package is something you install as a dependency and use via the import system. The packages on PyPI are an example of this.
An application or app is an end product that other external code does not directly rely on via the import system (i.e. they are standalone). Desktop applications, command-line tools, etc. are examples of applications.
A lock file records the packages that are to be installed for an
app. Traditionally, the exact version of the package to be installed
is specified by a lock file, but specified packages are not always
installed on a given platform (according a filtering logic described
in a later section), which enables the lock file to describe
reproducibility across multiple platforms. Examples of this are
package-lock.json from npm,
Poetry.lock from Poetry, etc.
Locking is the act of taking the input of the packages an app depends on and producting a lock file from that.
A locker is a tool which produces a lock file.
An installer consumes a lock file to install what the lock file specifies.
Applications want reproducible installs for a few reasons (we are not worrying about package development, integration into larger systems that would handle locking dependencies external to the Python application, or other situations where flexible installation requirements are desired over strict, reproducible installations).
One, reproducibility eases development. When you and your fellow developers all end up with the same files on a specific platform, you make sure you are all developing towards the same experience for the application. You also want your users to install the same files as you expect to guarantee the experience is the same as you developed for them.
Two, you want to be able to reproduce what gets installed across multiple platforms. Thanks to Python’s portability across operating systems, CPUs, etc., it is very easy and often desirable to create applications that are not restricted to a single platform. Thus, you want to be flexible enough to allow for differences in your package dependencies between platforms, while still having consistency and reproducibility on any one specific platform.
Three, reproducibility is more secure. When you control exactly what files are installed, you can make sure no malicious actor is attempting to slip nefarious code into your application (i.e. some supply chain attacks). By using a lock file which always leads to reproducible installs, we can avoid certain risks entirely.
Four, relying on the wheel file format provides reproducibility without requiring build tools to support reproducibility themselves. Thanks to wheels being static and not executing code as part of installation, wheels always lead to a reproducible result. Compare this to source distributions (aka sdists) or source trees which only lead to a reproducible install if their build tool supports reproducibility due to inherent code execution. Unfortunately the vast majority of build tools do not support reproducible builds, so this PEP helps alleviate that issue by only supporting wheels as a package format.
This PEP proposes a standard for a lock file, as the current solutions don’t meet the outlined goals. Today, the closest we come to a lock file standard is the requirements file format from pip. Unfortunately, that format does not lead to inherently reproducible installs (it requires optional features both in the requirements file and the installer itself, to be discussed later).
The community itself has also shown a need for lock files based on the fact that multiple tools have independently created their own lock file formats:
Unfortunately, those tools all use differing lock file formats. This means tooling around these tools must be unique. This impacts tooling such as code editors and hosting providers, which want to be as flexible as possible when it comes to accepting a user’s application code, but also have a limit as to how much development resources they can spend to add support for yet another lock file format. A standardized format would allow tools to focus their work on a single target, and make sure that workflow decisions made by developers outside of the lock file format are of no concern to e.g. hosting providers.
Other programming language communities have also shown the usefulness of lock files by developing their own solution to this problem. Some of those communities include:
The trend in programming languages in the past decade seems to have been toward providing a lock file solution.
We wanted the file format to be easy to read as a diff when auditing
a change to the lock file. As such, and thanks to PEP 518 and
pyproject.toml, we decided to go with the TOML file format.
Secure by Design
Viewing the requirements file format as the closest we have to a lock file standard, there are a few issues with the file format when it comes to security. First is that the file format simply does not require you to specify the exact version of a package. This is why tools like pip-tools exist to help manage that users of requirements files.
Second, you must opt into specifying what files are acceptable to be
installed by using the
--hash argument for a specific dependency.
This is also optional with pip-tools as it requires specifying the
--generate-hashes CLI argument. This requires
for pip to make sure no dependencies lack a hash to check.
Third, even when you control what files may be installed, it does not
prevent other packages from being installed. If a dependency is not
listed in the requirements file, pip will happily go searching for a
file to meet that need. You must specify
--no-deps as an
argument to pip to prevent unintended dependency resolution outside
of the requirements file.
Fourth, the format allows for installing a
source distribution file (aka “sdist”). By its very nature,
installing an sdist requires executing arbitrary Python code, meaning
that there is no control over what files may be installed. Only by
--only-binary :all: can you guarantee pip to only use a
wheel file for each package.
To recap, in order for a requirements file to be as secure as what is being proposed, a user should always do the following steps:
- Use pip-tools and its command
- Install the requirements file using
pip install --require-hashes --no-deps --only-binary :all:
Critically, all of those flags, and both the specificity and exhaustion of what to install that pip-tools provides, are optional for requirements files.
As such, the proposal raised in this PEP is secure by design which combats some supply chain attacks. Hashes for files which would be used to install from are required. You can only install from wheels to unambiguously define what files will be placed in the file system. Installers must lead to an deterministic installation from a lock file for a given platform. All of this leads to a reproducible installation which you can deem trustworthy (when you have audited the lock file and what it lists).
Various projects which already have a lock file, like PDM and Poetry, provide a lock file which is cross-platform. This allows for a single lock file to work on multiple platforms while still leading to the exact same top-level requirements to be installed everywhere with the installation being consistent/unambiguous on each platform.
As to why this is useful, let’s use an example involving PyWeek (a week-long game development competition). Assume you are developing on Linux, while someone you choose to partner with is using macOS. Now assume the judges are using Windows. How do you make sure everyone is using the same top-level dependencies, while allowing for any platform-specific requirements (e.g. a package requires a helper package under Windows)?
With a cross-platform lock file, you can make sure that the key requirements are met consistently across all platforms. You can then also make sure that all users on the same platform get the same reproducible installation.
The separation of concerns between a locker and an installer allows for an installer to have a much simpler operation to perform. As such, it not only allows for installers to be easier to write, but facilitates in making sure installers create unambiguous, reproducible installations correctly.
The installer can also expend less computation/energy in creating the installation. This is beneficial not only for faster installs, but also from an energy consumption perspective, as installers are expected to be run more often than lockers.
This has led to a design where the locker must do more work upfront to the benefit installers. It also means the complexity of package dependencies is simpler and easier to comprehend in a lock files to avoid ambiguity.
Lock files MUST use the TOML file format. This not only prevents the
need to have another file format in the Python packaging ecosystem
thanks to its adoption by PEP 518 for
pyproject.toml, but also
assists in making lock files more human-readable.
Lock files MUST end their file names with
.toml part unambiguously distinguishes the format of the file,
and helps tools like code editors support the file appropriately. The
.pylock part distinguishes the file from other TOML files the user
has, to make the logic easier for tools to create functionality
specific to Python lock files, instead of TOML files in general.
The following sections are the top-level keys of the TOML file data format. Any field not listed as required is considered optional.
This field is required.
The version of the lock file being used. The key MUST be a string
consisting of a number that follows the same formatting as the
Metadata-Version key in the core metadata spec.
The value MUST be set to
"1.0" until a future PEP allows for a
different value. The introduction of a new optional key to the file
format SHOULD increase the minor version. The introduction of a new
required key or changing the format MUST increase the major version.
How to handle other scenarios is left as a per-PEP decision.
Installers MUST warn the user if the lock file specifies a version
whose major version is supported but whose minor version is
unsupported/unrecognized (e.g. the installer supports
the lock file specifies
Installers MUST raise an error if the lock file specifies a major
version which is unsupported (e.g. the installer supports
but the lock file specifies
This field is required.
The timestamp for when the lock file was generated (using TOML’s native timestamp type). It MUST be recorded using the UTC time zone to avoid ambiguity.
If the SOURCE_DATE_EPOCH environment variable is set, it MUST be used as the timestamp by the locker. This facilitates reproducibility of the lock file itself.
Tools may create their own sub-tables under the
tool table. The
rules for this table match those for
pyproject.toml and its
[tool] table from the build system declaration spec.
This table is required.
A table containing data applying to the overall lock file.
A key storing a string containing an environment marker as specified in the dependency specifier spec.
The locker MAY specify an environment marker which specifies any restrictions the lock file was generated under.
If the installer is installing for an environment which does not satisfy the specified environment marker, the installer MUST raise an error as the lock file does not support the target installation environment.
A key storing a string specifying platform compatibility tags (i.e. wheel tags). The tag MAY be a compressed tag set.
If the installer is installing for an environment which does not satisfy the specified tag (set), the installer MUST raise an error as the lock file does not support the targeted installation environment.
This field is required.
An array of strings following the dependency specifier spec. This array represents the top-level package dependencies of the lock file and thus the root of the dependency graph.
A string specifying the supported version(s) of Python for this lock
file. It follows the same format as that specified for the
Requires-Python field in the core metadata spec.
This array is required.
An array per package and version containing entries for the potential
(wheel) files to install (as represented by
Lockers MUST normalize a project’s name according to the simple repository API. If extras are specified as part of the project to install, the extras are to be included in the key name and are to be sorted in lexicographic order.
Within the file, the tables for the projects SHOULD be sorted by:
- Project/key name in lexicographic order
- Package version, newest/highest to older/lowest according to the version specifiers spec
- Optional dependencies (extras) via lexicographic order
- File name based on the
filenamefield (discussed below)
These recommendations are to help minimize diff changes between tool executions.
This field is required.
A string representing the base name of the file as represented by an
entry in the array (i.e. what
pathlib.PurePath.name represents). This
field is required to simplify installers as the file name is required
to resolve wheel tags derived from the file name. It also guarantees
that the association of the array entry to the file it is meant for is
This table is required.
A table with keys specifying a hash algorithm and values as the hash
for the file represented by this entry in the
Lockers SHOULD list hashes in lexicographic order. This is to help minimize diff sizes and the potential to overlook hash value changes.
An installer MUST only install a file which matches one of the specified hashes.
A string representing a URL where to get the file.
The installer MAY support any schemes it wants for URLs. A URL with no scheme MUST be assumed to be a local file path (both relative paths to the lock file and absolute paths). Installers MUST support, at minimum, HTTPS URLs as well as local file paths.
An installer MAY choose to not use the URL to retrieve a file if a file matching the specified hash can be found using alternative means (e.g. on the file system in a cache directory).
A boolean representing whether an installer should consider the project installed “directly” as specified by the direct URL origin of installed distributions spec.
If the key is true, then the installer MUST follow the direct URL origin of installed distributions spec for recording the installation as “direct”.
A string specifying the support version(s) of Python for this file. It
follows the same format as that specified for the
Requires-Python field in the core metadata spec.
An array of strings following the dependency specifier spec which represent the dependencies of this file.
version = "1.0" created-at = 2021-10-19T22:33:45.520739+00:00 [tool] # Tool-specific table. [metadata] requires = ["mousebender", "coveragepy[toml]"] marker = "sys_platform == 'linux'" # As an example for coverage. requires-python = ">=3.7" [[package.attrs."21.2.0"]] filename = "attrs-21.2.0-py2.py3-none-any.whl" hashes.sha256 = "149e90d6d8ac20db7a955ad60cf0e6881a3f20d37096140088356da6c716b0b1" url = "https://files.pythonhosted.org/packages/20/a9/ba6f1cd1a1517ff022b35acd6a7e4246371dfab08b8e42b829b6d07913cc/attrs-21.2.0-py2.py3-none-any.whl" requires-python = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*" [[package.attrs."21.2.0"]] # If attrs had another wheel file (e.g. that was platform-specific), # it could be listed here. [[package."coveragepy[toml]"."6.2.0"]] filename = "coverage-6.2-cp310-cp310-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl" hashes.sha256 = "c7912d1526299cb04c88288e148c6c87c0df600eca76efd99d84396cfe00ef1d" url = "https://files.pythonhosted.org/packages/da/64/468ca923e837285bd0b0a60bd9a287945d6b68e325705b66b368c07518b1/coverage-6.2-cp310-cp310-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl" requires-python = ">=3.6" requires = ["tomli"] [[package."coveragepy[toml]"."6.2.0"]] filename = "coverage-6.2-cp310-cp310-musllinux_1_1_x86_64.whl " hashes.sha256 = "276651978c94a8c5672ea60a2656e95a3cce2a3f31e9fb2d5ebd4c215d095840" url = "https://files.pythonhosted.org/packages/17/d6/a29f2cccacf2315150c31d8685b4842a6e7609279939a478725219794355/coverage-6.2-cp310-cp310-musllinux_1_1_x86_64.whl" requires-python = ">=3.6" requires = ["tomli"] # More wheel files for `coverage` could be listed for more # extensive support (i.e. all Linux-based wheels). [[package.mousebender."2.0.0"]] filename = "mousebender-2.0.0-py3-none-any.whl" hashes.sha256 = "a6f9adfbd17bfb0e6bb5de9a27083e01dfb86ed9c3861e04143d9fd6db373f7c" url = "https://files.pythonhosted.org/packages/f4/b3/f6fdbff6395e9b77b5619160180489410fb2f42f41272994353e7ecf5bdf/mousebender-2.0.0-py3-none-any.whl" requires-python = ">=3.6" requires = ["attrs", "packaging"] [[package.packaging."20.9"]] filename = "packaging-20.9-py2.py3-none-any.whl" hashes.blake-256 = "3e897ea760b4daa42653ece2380531c90f64788d979110a2ab51049d92f408af" hashes.sha256 = "67714da7f7bc052e064859c05c595155bd1ee9f69f76557e21f051443c20947a" url = "https://files.pythonhosted.org/packages/3e/89/7ea760b4daa42653ece2380531c90f64788d979110a2ab51049d92f408af/packaging-20.9-py2.py3-none-any.whl" requires-python = ">=3.6" requires = ["pyparsing"] [[package.pyparsing."2.4.7"]] filename = "pyparsing-2.4.7-py2.py3-none-any.whl" hashes.sha256 = "ef9d7589ef3c200abe66653d3f1ab1033c3c419ae9b9bdb1240a85b024efc88b" url = "https://files.pythonhosted.org/packages/8a/bb/488841f56197b13700afd5658fc279a2025a39e22449b7cf29864669b15d/pyparsing-2.4.7-py2.py3-none-any.whl" direct = true # For demonstration purposes. requires-python = ">=2.6, !=3.0.*, !=3.1.*, !=3.2.*" [[package.tomli."2.0.0"]] filename = "tomli-2.0.0-py3-none-any.whl" hashes.sha256 = "b5bde28da1fed24b9bd1d4d2b8cba62300bfb4ec9a6187a957e8ddb9434c5224" url = "https://files.pythonhosted.org/packages/e2/9f/5e1557a57a7282f066351086e78f87289a3446c47b2cb5b8b2f614d8fe99/tomli-2.0.0-py3-none-any.whl" requires-python = ">=3.7"
Expectations for Lockers
Lockers MUST create lock files for which a topological sort of the packages which qualify for installation on the specified platform results in a graph for which only a single version of any package qualifies for installation and there is at least one compatible file to install for each package. This leads to a lock file for any supported platform where the only decision an installer can make is what the “best-fitting” wheel is to install (which is discussed below).
Lockers are expected to utilize
metadata.requires-python as appropriate as well as environment
markers specified via
requires and Python version requirements via
requires-python to enforce this result for installers. Put another
way, the information used in the lock file is not expected to be
pristine/raw from the locker’s input and instead is to be changed as
necessary to the benefit of the locker’s goals.
Expectations for Installers
The expected algorithm for resolving what to install is:
- Construct a dependency graph based on the data in the lock file
metadata.requiresas the starting/root point.
- Eliminate all files that are unsupported by the specified platform.
- Eliminate all irrelevant edges between packages based on marker
- Raise an error if a package version is still reachable from the root of the dependency graph but lacks any compatible file.
- Verify that all packages left only have one version to install, raising an error otherwise.
- Install the best-fitting wheel file for each package which remains.
Installers MUST follow a deterministic algorithm determine what the
“best-fitting wheel file” is. A simple solution for this is to
rely upon the packaging project
packaging.tags module to determine wheel file precedence.
Installers MUST support installing into an empty environment. Installers MAY support installing into an environment that already contains installed packages (and whatever that would entail to be supported).
(Potential) Tool Support
The pip team has said they are interested in supporting this PEP if accepted. The current proposal for pip may even supplant the need for pip-tools.
PDM has also said they would support the PEP if accepted.
Pyflow has said they “like the idea” of the PEP.
Poetry has said they would not support the PEP as-is because
“Poetry supports sdists files, directory and VCS dependencies which are not supported”.
Recording requirements at the file level, which is on purpose to
better reflect what can occur when it comes to dependencies,
“is contradictory to the design of Poetry”.
This also excludes export support to a this PEP’s lock file as
“Poetry exports the information present in the poetry.lock file into another format”
and sdists and source trees are included in
Thus it is not a clean translation from Poetry’s lock file to this
PEP’s lock file format.
As there is no pre-existing specification regarding lock files, there are no explicit backwards compatibility concerns.
As for pre-existing tools that have their own lock file, some updating
will be required. Most document the lock file name, but not its
contents. For projects which do not commit their lock file to
version control, they will need to update the equivalent of their
.gitignore file. For projects that do commit their lock file to
version control, what file(s) get committed will need an update.
For projects which do document their lock file format like pipenv, they will very likely need a major version release which changes the lock file format.
In general, this PEP could be considered successful if:
- Two pre-existing tools became lockers (e.g. pip-tools, PDM,
- Pip became an installer.
- One major, non-Python-specific platform supported the file format (e.g. a cloud provider).
This would show interoperability, usability, and programming community/business acceptance.
In terms of a transition plan, there are potentially multiple steps that could lead to this desired outcome. Below is a somewhat idealized plan that would see this PEP being broadly used.
pip freeze equivalent tool could be developed which
creates a lock file. While installed packages do not by themselves
provide enough information to statically create a lock file, a user
could provide local directories and index URLs to construct one. This
would then lead to lock files that are stricter than a requirements
file by limiting the lock file to the current platform. This would
also allow people to see whether their environment would be
Second, a stand-alone installer should be developed. As the requirements on an installer are much simpler than what pip provides, it should be reasonable to have an installer that is independently developed.
Third, a tool to convert a pinned requirements file as emitted by
pip-tools could be developed. Much like the
pip freeze equivalent
outlined above, some input from the user may be needed. But this tool
could act as a transitioning step for anyone who has an appropriate
requirements file. This could also act as a test before potentially
having pip-tools grow some
--lockfile flag to use this PEP.
All of this could be required before the PEP transitions from conditional acceptance to full acceptance (and give the community a chance to test if this PEP is potentially useful).
At this point, the goal would be to increase interoperability between tools.
First, pip would become an installer. By having the most widely used installer support the format, people can innovate on the locker side while knowing people will have the tools necessary to actually consume a lock file.
Second, pip becomes a locker. Once again, pip’s reach would make the format accessible for the vast majority of Python users very quickly.
Third, a project with a pre-existing lock file format supports at least exporting to the lock file format (e.g. PDM or Pyflow). This would show that the format meets the needs of other projects.
With the tooling available throughout the community, acceptance would be shown via those not exclusively tied to the Python community supporting the file format based on what they believe their users want.
First, tools that operate on requirements files like code editors having equivalent support for lock files.
Second, consumers of requirements files like cloud providers would also accept lock files.
At this point the PEP would have permeated out far enough to be on par with requirements files in terms of general accpetance and potentially more if projects had dropped their own lock files for this PEP.
A lock file should not introduce security issues but instead help solve them. By requiring the recording of hashes for files, a lock file is able to help prevent tampering with code since the hash details were recorded. Relying on only wheel files means what files will be installed can be known ahead of time and is reproducible. A lock file also helps prevent unexpected package updates being installed which may in turn be malicious.
How to Teach This
Teaching of this PEP will very much be dependent on the lockers and installers being used for day-to-day use. Conceptually, though, users could be taught that a lock file specifies what should be installed for a project to work. The benefits of consistency and security should be emphasized to help users realize why they should care about lock files.
A proof-of-concept locker can be found at https://github.com/frostming/pep665_poc . No installer has been implemented yet, but the design of this PEP suggests the locker is the more difficult aspect to implement.
File Formats Other Than TOML
JSON was briefly considered, but due to:
- TOML already being used for
- TOML being more human-readable
- TOML leading to better diffs
the decision was made to go with TOML. There was some concern over
Python’s standard library lacking a TOML parser, but most packaging
tools already use a TOML parser thanks to
pyproject.toml so this
issue did not seem to be a showstopper. Some have also argued against
this concern in the past by the fact that if packaging tools abhor
installing dependencies and feel they can’t vendor a package then the
packaging ecosystem has much bigger issues to rectify than the need to
depend on a third-party TOML parser.
Alternative Naming Schemes
Specifying a directory to install file to was considered, but ultimately rejected due to people’s distaste for the idea.
It was also suggested to not have a special file name suffix, but it was decided that hurt discoverability by tools too much.
Supporting a Single Lock File
At one point the idea of only supporting single lock file which contained all possible lock information was considered. But it quickly became apparent that trying to devise a data format which could encompass both a lock file format which could support multiple environments as well as strict lock outcomes for reproducible builds would become quite complex and cumbersome.
The idea of supporting a directory of lock files as well as a single
lock file named
pyproject-lock.toml was also considered. But any
possible simplicity from skipping the directory in the case of a
single lock file seemed unnecessary. Trying to define appropriate
logic for what should be the
pyproject-lock.toml file and what
should go into
pyproject-lock.d seemed unnecessarily complicated.
Using a Flat List Instead of a Dependency Graph
The first version of this PEP proposed that the lock file have no concept of a dependency graph. Instead, the lock file would list exactly what should be installed for a specific platform such that installers did not have to make any decisions about what to install, only validating that the lock file would work for the target platform.
This idea was eventually rejected due to the number of combinations of potential PEP 508 environment markers. The decision was made that trying to have lockers generate all possible combinations as individual lock files when a project wants to be cross-platform would be too much.
Alternative Names for
Some other names for what became
dependencies. Initially this PEP chose
after asking a Python beginner which term they preferred. But based
on feedback on an earlier draft of this PEP,
requires was chosen
as the term.
Accepting PEP 650
PEP 650 was an earlier attempt at trying to tackle this problem by specifying an API for installers instead of standardizing on a lock file format (ala PEP 517). The initial response to PEP 650 could be considered mild/lukewarm. People seemed to be consistently confused over which tools should provide what functionality to implement the PEP. It also potentially incurred more overhead as it would require executing Python APIs to perform any actions involving packaging.
This PEP chooses to standardize around an artifact instead of an API (ala PEP 621). This would allow for more tool integrations as it removes the need to specifically use Python to do things such as create a lock file, update it, or even install packages listed in a lock file. It also allows for easier introspection by forcing dependency graph details to be written in a human-readable format. It also allows for easier sharing of knowledge by standardizing what people need to know more (e.g. tutorials become more portable between tools when it comes to understanding the artifact they produce). It’s also simply the approach other language communities have taken and seem to be happy with.
Acceptance of this PEP would mean PEP 650 gets rejected.
Specifying Requirements per Package Instead of per File
An earlier draft of this PEP specified dependencies at the package level instead of per file. While this has traditionally been how packaging systems work, it actually did not reflect accurately how things are specified. As such, this PEP was subsequently updated to reflect the granularity that dependencies can truly be specified at.
Specify Where Lockers Gather Input
This PEP does not specify how a locker gets its input. An initial suggestion was to partially reuse PEP 621, but due to disagreements on how flexible the potential input should be in terms of specifying things such as indexes, etc., it was decided this would best be left to a separate PEP.
Allowing Source Distributions and Source Trees to be an Opt-In, Supported File Format
After extensive discussion, it was decided that this PEP would not support source distributions (aka sdists) or source trees as an acceptable format for code. Introducing sdists and source trees to this PEP would immediately undo the reproducibility and security goals due to needing to execute code to build the sdist or source tree. It would also greatly increase the complexity for (at least) installers as the dynamic build nature of sdists and source trees means the installer would need to handle fully resolving whatever requirements the sdists produced dynamically, both from a building and installation perspective.
Due to all of this, it was decided it was best to have a separate discussion about what supporting sdists and source trees after this PEP is accepted/rejected. As the proposed file format is versioned, introducing sdists and source tree support in a later PEP is doable.
It should be noted, though, that this PEP is not stop an out-of-band solution from being developed to be used in conjunction with this PEP. Building wheel files from sdists and shipping them with code upon deployment so they can be included in the lock file is one option. Another is to use a requirements file just for sdists and source trees, then relying on a lock file for all wheels.
Thanks to Frost Ming of PDM and Sébastien Eustace of Poetry for providing input around dynamic install-time resolution of PEP 508 requirements.
Thanks to Kushal Das for making sure reproducible builds stayed a concern for this PEP.
Thanks to Andrea McInnes for initially settling the bikeshedding and
choosing the paint colour of
needs (at which point people ralled
requires colour instead).
This document is placed in the public domain or under the CC0-1.0-Universal license, whichever is more permissive.
Last modified: 2022-03-26 21:05:34 GMT