Features Reference

PyO3 provides a number of Cargo features to customise 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


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.


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.

abi3-py36 / abi3-py37 / abi3-py38 / abi3-py39

These features are an extension 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.

Features for embedding Python in Rust


This feature changes Python::with_gil and Python::acquire_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


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

  • #[pymodule]
  • #[pyfunction]
  • #[pyclass]
  • #[pymethods]
  • #[pyproto]
  • #[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.


This feature enables a dependency on inventory, which enables each #[pyclass] to have more than one #[pymethods] block.

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.


The nightly feature needs the nightly Rust compiler. This allows PyO3 to use Rust's unstable specialization feature to apply the following optimizations:

  • FromPyObject for Vec and [T;N] can perform a memcpy when the object supports the Python buffer protocol.
  • ToBorrowedObject can skip a reference count increase when the provided object is a Python native type.


The resolve-config feature of the pyo3-build-config crate controls whether that crate's build script automatically resolves a Python interpreter / build configuration. Disabling this feature enables this crate to be used in library mode. This may be desirable for use cases where you want 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.


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


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


This feature adds a dependency on num-bigint and enables conversions into its BigInt and BigUint types.


This feature adds a dependency on num-complex and enables conversions into its Complex type.


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


fn main() {
#[derive(Serialize, Deserialize)]
struct Permission {
    name: String

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