Features reference

PyO3 provides a number of Cargo features to customize functionality. This chapter of the guide provides detail on each of them.

By default, only the macros feature is enabled.

Features for extension module authors

extension-module

This feature is required when building a Python extension module using PyO3.

It tells PyO3's build script to skip linking against libpython.so on Unix platforms, where this must not be done.

See the building and distribution section for further detail.

abi3

This feature is used when building Python extension modules to create wheels which are compatible with multiple Python versions.

It restricts PyO3's API to a subset of the full Python API which is guaranteed by PEP 384 to be forwards-compatible with future Python versions.

See the building and distribution section for further detail.

The abi3-pyXY features

(abi3-py37, abi3-py38, abi3-py39, abi3-py310 and abi3-py311)

These features are extensions of the abi3 feature to specify the exact minimum Python version which the multiple-version-wheel will support.

See the building and distribution section for further detail.

generate-import-lib

This experimental feature is used to generate import libraries for Python DLL for MinGW-w64 and MSVC (cross-)compile targets.

Enabling it allows to (cross-)compile extension modules to any Windows targets without having to install the Windows Python distribution files for the target.

See the building and distribution section for further detail.

Features for embedding Python in Rust

auto-initialize

This feature changes Python::with_gil to automatically initialize a Python interpreter (by calling prepare_freethreaded_python) if needed.

If you do not enable this feature, you should call pyo3::prepare_freethreaded_python() before attempting to call any other Python APIs.

Advanced Features

experimental-async

This feature adds support for async fn in #[pyfunction] and #[pymethods].

The feature has some unfinished refinements and performance improvements. To help finish this off, see issue #1632 and its associated draft PRs.

experimental-declarative-modules

This feature allows to declare Python modules using #[pymodule] mod my_module { ... } syntax.

The feature has some unfinished refinements and edge cases. To help finish this off, see issue #3900.

experimental-inspect

This feature adds the pyo3::inspect module, as well as IntoPy::type_output and FromPyObject::type_input APIs to produce Python type "annotations" for Rust types.

This is a first step towards adding first-class support for generating type annotations automatically in PyO3, however work is needed to finish this off. All feedback and offers of help welcome on issue #2454.

gil-refs

This feature is a backwards-compatibility feature to allow continued use of the "GIL Refs" APIs deprecated in PyO3 0.21. These APIs have performance drawbacks and soundness edge cases which the newer Bound<T> smart pointer and accompanying APIs resolve.

This feature and the APIs it enables is expected to be removed in a future PyO3 version.

py-clone

This feature was introduced to ease migration. It was found that delayed reference counts cannot be made sound and hence Cloning an instance of Py<T> must panic without the GIL being held. To avoid migrations introducing new panics without warning, the Clone implementation itself is now gated behind this feature.

pyo3_disable_reference_pool

This is a performance-oriented conditional compilation flag, e.g. set via $RUSTFLAGS, which disabled the global reference pool and the assocaited overhead for the crossing the Python-Rust boundary. However, if enabled, Dropping an instance of Py<T> without the GIL being held will abort the process.

macros

This feature enables a dependency on the pyo3-macros crate, which provides the procedural macros portion of PyO3's API:

  • #[pymodule]
  • #[pyfunction]
  • #[pyclass]
  • #[pymethods]
  • #[derive(FromPyObject)]

It also provides the py_run! macro.

These macros require a number of dependencies which may not be needed by users who just need PyO3 for Python FFI. Disabling this feature enables faster builds for those users, as these dependencies will not be built if this feature is disabled.

This feature is enabled by default. To disable it, set default-features = false for the pyo3 entry in your Cargo.toml.

multiple-pymethods

This feature enables a dependency on inventory, which enables each #[pyclass] to have more than one #[pymethods] block. This feature also requires a minimum Rust version of 1.62 due to limitations in the inventory crate.

Most users should only need a single #[pymethods] per #[pyclass]. In addition, not all platforms (e.g. Wasm) are supported by inventory. For this reason this feature is not enabled by default, meaning fewer dependencies and faster compilation for the majority of users.

See the #[pyclass] implementation details for more information.

nightly

The nightly feature needs the nightly Rust compiler. This allows PyO3 to use the auto_traits and negative_impls features to fix the Python::allow_threads function.

resolve-config

The resolve-config feature of the pyo3-build-config crate controls whether that crate's build script automatically resolves a Python interpreter / build configuration. This feature is primarily useful when building PyO3 itself. By default this feature is not enabled, meaning you can freely use pyo3-build-config as a standalone library to read or write PyO3 build configuration files or resolve metadata about a Python interpreter.

Optional Dependencies

These features enable conversions between Python types and types from other Rust crates, enabling easy access to the rest of the Rust ecosystem.

anyhow

Adds a dependency on anyhow. Enables a conversion from anyhow’s Error type to PyErr, for easy error handling.

chrono

Adds a dependency on chrono. Enables a conversion from chrono's types to python:

chrono-tz

Adds a dependency on chrono-tz. Enables conversion from and to Tz. It requires at least Python 3.9.

either

Adds a dependency on either. Enables a conversions into either’s Either type.

eyre

Adds a dependency on eyre. Enables a conversion from eyre’s Report type to PyErr, for easy error handling.

hashbrown

Adds a dependency on hashbrown and enables conversions into its HashMap and HashSet types.

indexmap

Adds a dependency on indexmap and enables conversions into its IndexMap type.

num-bigint

Adds a dependency on num-bigint and enables conversions into its BigInt and BigUint types.

num-complex

Adds a dependency on num-complex and enables conversions into its Complex type.

num-rational

Adds a dependency on num-rational and enables conversions into its Ratio type.

rust_decimal

Adds a dependency on rust_decimal and enables conversions into its Decimal type.

serde

Enables (de)serialization of Py<T> objects via serde. This allows to use #[derive(Serialize, Deserialize) on structs that hold references to #[pyclass] instances

#[cfg(feature = "serde")]
#[allow(dead_code)]
mod serde_only {
use pyo3::prelude::*;
use serde::{Deserialize, Serialize};

#[pyclass]
#[derive(Serialize, Deserialize)]
struct Permission {
    name: String,
}

#[pyclass]
#[derive(Serialize, Deserialize)]
struct User {
    username: String,
    permissions: Vec<Py<Permission>>,
}
}

smallvec

Adds a dependency on smallvec and enables conversions into its SmallVec type.