pyproject.toml
#
New in version 10.0.
Modern Python packages can contain a
pyproject.toml
file, first introduced in
PEP 518
and later expanded in
PEP 517
,
PEP 621
and
PEP 660
. This file contains build system requirements and information, which are used by pip to build the package.
The overall process for building a package is:
Create an isolated build environment.
Populate the build environment with build dependencies.
Generate the package’s metadata, if necessary and possible.
Generate a wheel for the package.
The wheel can then be used to perform an installation, if necessary.
For building packages using this interface, pip uses an
isolated environment
. That is, pip will install build-time Python dependencies in a temporary directory which will be added to
sys.path
for the build commands. This ensures that build requirements are handled independently of the user’s runtime environment.
For example, a project that needs an older version of setuptools to build can still be installed, even if the user has an newer version installed (and without silently replacing that version).
Introduced in
PEP 518
，
build-system.requires
key in the
pyproject.toml
file is a list of requirement specifiers for build-time dependencies of a package.
[build-system] requires = ["setuptools ~= 58.0", "cython ~= 0.29.0"]
It is also possible for a build backend to provide dynamically calculated build dependencies, using
PEP 517
’s
get_requires_for_build_wheel
hook. This hook will be called by pip, and dependencies it describes will also be installed in the build environment. For example, newer versions of setuptools expose the contents of
setup_requires
to pip via this hook.
Build-time requirement specifiers follow PEP 508 , so it’s possible to reference packages with URLs. For example:
[build-system] requires = ["setuptools @ git+https://github.com/pypa/setuptools.git@main"]
New in version 19.0.
Once the build environment has been created and populated with build-time dependencies,
pip
will usually need metadata about a package (name, version, dependencies, and more).
若
PEP 517
’s
prepare_metadata_for_build_wheel
hook is provided by the build backend, that will be used to generate the packages’ metadata. Otherwise, a wheel will be generated (as described below) and the metadata contained within such a wheel will be used.
New in version 19.0.
For generating a wheel, pip uses the
PEP 517
build_wheel
hook that has to be provided by the build backend. The build backend will generate a wheel, which may involve compiling extension code written in C/C++ (or other languages).
Wheels generated using this mechanism can be cached for reuse, to speed up future installations.
New in version 21.3.
For performing editable installs, pip will use
PEP 660
build_wheel_for_editable
hook that has to be provided by the build backend. The wheels generated using this mechanism are not cached.
Compatibility fallback
If this hook is missing on the build backend
and
there’s a
setup.py
file in the project, pip will fallback to the legacy setup.py-based editable installation.
This is considered a stopgap solution until setuptools adds support for PEP 660 , at which point this functionality will be removed; following pip’s regular deprecation policy .
Build backends have the ability to accept configuration settings, which can change the way the build is handled. These settings take the form of a series of
key=value
pairs. The user can supply configuration settings using the
--config-settings
command line option (which can be supplied multiple times, in order to specify multiple settings).
The supplied configuration settings are passed to every backend hook call.
It is the responsibility of the build backend to ensure that the output is in the correct encoding, as described in PEP 517 . This likely involves dealing with the same challenges as pip has for legacy builds .
If a project does not have a
pyproject.toml
file containing a
build-system
section, it will be assumed to have the following backend settings:
[build-system] requires = ["setuptools>=40.8.0", "wheel"] build-backend = "setuptools.build_meta:__legacy__"
If a project has a
build-system
section but no
build-backend
, then:
It is expected to include
setuptools
and
wheel
as build requirements. An error is reported if the available version of
setuptools
is not recent enough.
The
setuptools.build_meta:__legacy__
build backend will be used.
This can be disabled using the
--no-build-isolation
flag -- users supplying this flag are responsible for ensuring the build environment is managed appropriately, including ensuring that all required build-time dependencies are installed, since pip does not manage build-time dependencies when this flag is passed.
As this feature was incrementally rolled out, there have been various notable changes and improvements in it.
setuptools 40.8.0 is the first version of setuptools that offers a
PEP 517
backend that closely mimics directly executing
setup.py
.
Prior to pip 18.0, pip only supports installing build requirements from wheels, and does not support the use of environment markers and extras (only version specifiers are respected).
Prior to pip 18.1, build dependencies using
.pth
files are not properly supported; as a result namespace packages do not work under Python 3.2 and earlier.