Crate Configuration

Build Artifacts for pyembed

The pyembed crate needs to reference special artifacts as part of its build process in order to compile a Python interpreter into a binary. The most important of these artifacts is a library providing Python symbols.

By default, the pyembed crate’s build.rs build script will run pyoxidizer run-build-script, which will attempt to find a PyOxidizer config file and evaluate its default build script target. Using environment variables set by cargo and by the build.rs script, artifacts will be placed in the correct locations and pyembed will be built seemingly like any normal Rust crate.

The special build artifacts are generated by resolving a configuration file target returning a PythonEmbeddedResources instance. In the auto-generated configuration file, the embedded target returns such a type.

Cargo Features to Control Building

The pyembed crate and generated Rust projects share a set of build-mode-* Cargo feature flags to control how build artifacts are created and consumed.

The features are described in the following sections.

build-mode-standalone

Do not attempt to invoke pyoxidizer or find artifacts it would have built. It is possible to build the pyembed crate in this mode if the rust-cpython and python3-sys crates can find a Python interpreter. But, the pyembed crate may not be usable or work in the way you want it to.

This mode is intended to be used for performing quick testing on the pyembed crate. It is quite possible that linking errors will occur in this mode unless you take additional actions to point Cargo at appropriate libraries.

build-mode-pyoxidizer-exe

A pyoxidizer executable will be run to generate build artifacts.

The path to this executable can be defined via the PYOXIDIZER_EXE environment variable. Otherwise PATH will be used.

At build time, pyoxidizer run-build-script will be run. A PyOxidizer configuration file will be discovered using the heuristics described at Automatic File Location Strategy. OUT_DIR will be set if running from cargo, so a pyoxidizer.bzl next to the main Rust project being built should be found and used.

pyoxidizer run-build-script will resolve the default build script target by default. To override which target should be resolved, specify the target name via the PYOXIDIZER_BUILD_TARGET environment variable. e.g.:

$ PYOXIDIZER_BUILD_TARGET=build-artifacts cargo build

build-mode-prebuilt-artifacts

This mode tells the build script to reuse artifacts that were already built. (Perhaps you called pyoxidizer build or pyoxidizer run-build-script outside the context of a normal cargo build.)

In this mode, the build script will look for artifacts in the directory specified by PYOXIDIZER_ARTIFACT_DIR if set, falling back to OUT_DIR. This directory must have a cargo_metadata.txt file, which will be printed to stdout by the build script to tell Cargo how to link a Python library.

cpython-link-unresolved-static

Configures the link mode of the cpython crate to use a static pythonXY library without resolving the symbol at its own build time. The pyembed crate or a crate building it will need to emit cargo:rustc-link-lib=static=pythonXY and any cargo:rustc-link-search=native={} lines to specify an explicit pythonXY library to link against.

This is the link mode used to produce self-contained binaries containing libpython and pyembed code.

cpython-link-default

Configures the link mode of the cpython crate to use default semantics. The crate’s build script will find a pre-built Python library by querying the python defined by PYTHON_SYS_EXECUTABLE or found on PATH. See the cpython crate’s documentation for more.

This link mode should be used when linking against an existing libpython that can be found by the cpython crate’s build script.