# 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 to select the target ABI

Each version of CPython exposes an ABI corresponding to the C API that is particular to that version.
Extensions built for this "version-specific" ABI can only be imported by Python interpreters with the same major version, since the Python C API and ABI are subject to change in every major release.
Python also supports a [limited API](https://docs.python.org/3/c-api/stable.html#limited-c-api) and [stable ABI](https://docs.python.org/3/c-api/stable.html#stable-abi).
Extensions targeting the stable ABI defined by Python 3.X can be imported by any subsequent Python version newer than Python 3.X, but not older versions.

There are two "flavors" of stable ABI: `abi3`, supported on Python 3.2 and newer but *not* the free-threaded builds and `abi3t`, supported on Python 3.15 and newer for both the GIL-enabled and free-threaded builds of Python.
PyO3 supports building extensions targeting both flavors of stable ABI.

When PyO3 finds a "host" python interpreter and no `abi3` or `abi3t` feature is active, it will generate extensions targeting the version-specific ABI for the host Python version.
For example, when ``pip`` or ``uv`` installs a Python package that includes Rust dependencies that depend on PyO3, the host interpreter is the interpreter running ``pip`` or the interpreter from the activated ``uv`` environment.

To build for the stable ABIs, you must activate an `abi3` and/or an `abi3t` feature.
You can simultaneously activate both features.
This will produce an `abi3` extension on the GIL-enabled and a version-specific extension on Python 3.14 and an `abi3t` extension on Python 3.15 and newer.

### `abi3`

This feature is used when building Python extension modules to create wheels which are compatible with multiple Python versions but not the free-threaded build.

It restricts PyO3's API to a subset of the full Python API which is guaranteed by [PEP 384](https://www.python.org/dev/peps/pep-0384/) to be forwards-compatible with future Python versions.

Since no particular "target" Python version is implied by this feature, it will generate an `abi3` extension targeting the stable ABI defined by the "host" Python interpreter.
As such, this feature requires a host Python interpreter is present and cannot be used for cross-compilation.

If you are using this feature to distribute extensions, you should ensure your minimum supported Python version is installed to do the build.
However, see the description of the `abi3-pyXY` feature if you would like to generate extensions targeting an older Python version using a recent Python interpreter.

See the [building and distribution](building-and-distribution.md#py_limited_apiabi3abi3t) section for further detail.

### The `abi3-pyXY` features

(`abi3-py39`, `abi3-py310`, `abi3-py311`, `abi3-py312`, `abi3-py313`, `abi3-py314` and `abi3-py315`)

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

They can be used to target versions of the ABI defined by Python versions released before the "host" python interpreter.
They can also be used without any host interpreter at all to cross-compile.

See the [building and distribution](building-and-distribution.md#minimum-python-version-for-abi3-and-abi3t-builds) section for further detail.

### `abi3t`

This feature is used when building Python extension modules to create wheels which are compatible with Python 3.15 or newer, targeting both the free-threaded and GIL-enabled build with a single extension module.

It restricts PyO3's API to a subset of the full Python API which is guaranteed by [PEP 384](https://www.python.org/dev/peps/pep-0384/) and [PEP 803](https://www.python.org/dev/peps/pep-0803/) to be forwards-compatible with future Python versions and be importable by the free-threaded and GIL-enabled interpreter.

Since no particular "target" Python version is implied by this feature, it will generate an `abi3` extension targeting the stable ABI defined by the "host" Python interpreter.
As such, this feature requires a host Python interpreter is present and cannot be used for cross-compilation.

If you are using this feature to distribute extensions, you should ensure your minimum supported Python version is installed to do the build.
However, see the description of the `abi3t-pyXY` feature if you would like to generate extensions targeting an older Python version using a recent Python interpreter.

Activating an `abi3t` and targeting Python 3.14 and older is a no-op: the build will produce an extension but it will not be an `abi3t` extension, since `abi3t` is unsupported before Python 3.15.

See the [building and distribution](building-and-distribution.md#py_limited_apiabi3abi3t) section for further detail.

### The `abi3t-pyXY` features

(`abi3t-py315`)

These features are extensions of the `abi3t` feature to specify the exact minimum Python version which the multiple-version-wheel will support.

They can be used to target versions of the ABI defined by Python versions released before the "host" python interpreter.
They can also be used without any host interpreter at all to cross-compile.

Activating an `abi3t` and targeting Python 3.14 and older is a no-op: the build will produce an extension but it will not be an `abi3t` extension, since `abi3t` is unsupported before Python 3.15.

See the [building and distribution](building-and-distribution.md#minimum-python-version-for-abi3-and-abi3t-builds) section for further detail.

## Features for embedding Python in Rust

### `auto-initialize`

This feature changes [`Python::attach`]({{#PYO3_DOCS_URL}}/pyo3/marker/struct.Python.html#method.attach) to automatically initialize a Python interpreter (by calling [`Python::initialize`]({{#PYO3_DOCS_URL}}/pyo3/marker/struct.Python.html#method.initialize)) if needed.

If you do not enable this feature, you should call `Python::initialize()` 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](https://github.com/PyO3/pyo3/issues/1632) and its associated draft PRs.

### `experimental-inspect`

This feature adds to the built binaries introspection data that can be then retrieved using the `pyo3-introspection` crate to generate [type stubs](https://typing.readthedocs.io/en/latest/source/stubs.html).

Also, 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](https://github.com/PyO3/pyo3/issues/2454).

### `py-clone`

This feature was introduced to ease migration.
It was found that delayed reference counting (which PyO3 used historically) could not be made sound and hence `Clone`-ing an instance of `Py<T>` is impossible when not attached to Python interpreter (it will panic).
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`][set-configuration-options], which disabled the global reference pool and the associated overhead for the crossing the Python-Rust boundary.
However, if enabled, `Drop`ping an instance of `Py<T>` when not attached to the Python interpreter 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.

> [!NOTE]
> 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 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`, which is used in the implementation of the feature.
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](class.md#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::detach` function.

## 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](https://docs.rs/anyhow).
Enables a conversion from [anyhow](https://docs.rs/anyhow)’s [`Error`](https://docs.rs/anyhow/latest/anyhow/struct.Error.html) type to [`PyErr`]({{#PYO3_DOCS_URL}}/pyo3/struct.PyErr.html), for easy error handling.

### `arc_lock`

Enables Pyo3's `MutexExt` trait for all Mutexes that extend on [`lock_api::Mutex`](https://docs.rs/lock_api/latest/lock_api/struct.Mutex.html) or [`parking_lot::ReentrantMutex`](https://docs.rs/lock_api/latest/lock_api/struct.ReentrantMutex.html) and are wrapped in an [`Arc`](https://doc.rust-lang.org/std/sync/struct.Arc.html) type.
Like [`Arc<parking_lot::Mutex>`](https://docs.rs/parking_lot/latest/parking_lot/type.Mutex.html#method.lock_arc)

### `bigdecimal`

Adds a dependency on [bigdecimal](https://docs.rs/bigdecimal) and enables conversions into its [`BigDecimal`](https://docs.rs/bigdecimal/latest/bigdecimal/struct.BigDecimal.html) type.

### `bytes`

Adds a dependency on [bytes](https://docs.rs/bytes/latest/bytes) and enables conversions into its [`Bytes`](https://docs.rs/bytes/latest/bytes/struct.Bytes.html) type.

### `chrono`

Adds a dependency on [chrono](https://docs.rs/chrono).
Enables a conversion from [chrono](https://docs.rs/chrono)'s types to python:

- [TimeDelta](https://docs.rs/chrono/latest/chrono/struct.TimeDelta.html) -> [`PyDelta`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDelta.html)
- [FixedOffset](https://docs.rs/chrono/latest/chrono/offset/struct.FixedOffset.html) -> [`PyDelta`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDelta.html)
- [Utc](https://docs.rs/chrono/latest/chrono/offset/struct.Utc.html) -> [`PyTzInfo`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyTzInfo.html)
- [NaiveDate](https://docs.rs/chrono/latest/chrono/naive/struct.NaiveDate.html) -> [`PyDate`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDate.html)
- [NaiveTime](https://docs.rs/chrono/latest/chrono/naive/struct.NaiveTime.html) -> [`PyTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyTime.html)
- [DateTime](https://docs.rs/chrono/latest/chrono/struct.DateTime.html) -> [`PyDateTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDateTime.html)

### `chrono-local`

Enables conversion from and to [Local](https://docs.rs/chrono/latest/chrono/struct.Local.html) timezones.
The current system timezone as determined by [`iana_time_zone::get_timezone()`](https://docs.rs/iana-time-zone/latest/iana_time_zone/fn.get_timezone.html) will be used for conversions.

`chrono::DateTime<Local>` will convert from either of:

- `datetime` objects with `tzinfo` equivalent to the current system timezone.
- "naive" `datetime` objects (those without a `tzinfo`), as it is a convention that naive datetime objects should be treated as using the system timezone.

When converting to Python, `Local` tzinfo is converted to a `zoneinfo.ZoneInfo` matching the current system timezone.

### `chrono-tz`

Adds a dependency on [chrono-tz](https://docs.rs/chrono-tz).
Enables conversion from and to [`Tz`](https://docs.rs/chrono-tz/latest/chrono_tz/enum.Tz.html).

### `either`

Adds a dependency on [either](https://docs.rs/either).
Enables a conversions into [either](https://docs.rs/either)’s [`Either`](https://docs.rs/either/latest/either/enum.Either.html) type.

### `eyre`

Adds a dependency on [eyre](https://docs.rs/eyre).
Enables a conversion from [eyre](https://docs.rs/eyre)’s [`Report`](https://docs.rs/eyre/latest/eyre/struct.Report.html) type to [`PyErr`]({{#PYO3_DOCS_URL}}/pyo3/struct.PyErr.html), for easy error handling.

### `hashbrown`

Adds a dependency on [hashbrown](https://docs.rs/hashbrown) and enables conversions into its [`HashMap`](https://docs.rs/hashbrown/latest/hashbrown/struct.HashMap.html) and [`HashSet`](https://docs.rs/hashbrown/latest/hashbrown/struct.HashSet.html) types.

### `indexmap`

Adds a dependency on [indexmap](https://docs.rs/indexmap) and enables conversions into its [`IndexMap`](https://docs.rs/indexmap/latest/indexmap/map/struct.IndexMap.html) type.

### `jiff-02`

Adds a dependency on [jiff@0.2](https://docs.rs/jiff/0.2).
Enables a conversion from [jiff](https://docs.rs/jiff)'s types to python:

- [SignedDuration](https://docs.rs/jiff/0.2/jiff/struct.SignedDuration.html) -> [`PyDelta`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDelta.html)
- [TimeZone](https://docs.rs/jiff/0.2/jiff/tz/struct.TimeZone.html) -> [`PyTzInfo`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyTzInfo.html)
- [Offset](https://docs.rs/jiff/0.2/jiff/tz/struct.Offset.html) -> [`PyTzInfo`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyTzInfo.html)
- [Date](https://docs.rs/jiff/0.2/jiff/civil/struct.Date.html) -> [`PyDate`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDate.html)
- [Time](https://docs.rs/jiff/0.2/jiff/civil/struct.Time.html) -> [`PyTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyTime.html)
- [DateTime](https://docs.rs/jiff/0.2/jiff/civil/struct.DateTime.html) -> [`PyDateTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDateTime.html)
- [Zoned](https://docs.rs/jiff/0.2/jiff/struct.Zoned.html) -> [`PyDateTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDateTime.html)
- [Timestamp](https://docs.rs/jiff/0.2/jiff/struct.Timestamp.html) -> [`PyDateTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDateTime.html)
- [ISOWeekDate](https://docs.rs/jiff/0.2/jiff/civil/struct.ISOWeekDate.html) -> [`PyDate`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDate.html)

### `lock_api`

Adds a dependency on [lock_api](https://docs.rs/lock_api) and enables Pyo3's `MutexExt` trait for all mutexes that extend on [`lock_api::Mutex`](https://docs.rs/lock_api/latest/lock_api/struct.Mutex.html) and [`parking_lot::ReentrantMutex`](https://docs.rs/lock_api/latest/lock_api/struct.ReentrantMutex.html) (like `parking_lot` or `spin`).

### `num-bigint`

Adds a dependency on [num-bigint](https://docs.rs/num-bigint) and enables conversions into its [`BigInt`](https://docs.rs/num-bigint/latest/num_bigint/struct.BigInt.html) and [`BigUint`](https://docs.rs/num-bigint/latest/num_bigint/struct.BigUint.html) types.

### `num-complex`

Adds a dependency on [num-complex](https://docs.rs/num-complex) and enables conversions into its [`Complex`](https://docs.rs/num-complex/latest/num_complex/struct.Complex.html) type.

### `num-rational`

Adds a dependency on [num-rational](https://docs.rs/num-rational) and enables conversions into its [`Ratio`](https://docs.rs/num-rational/latest/num_rational/struct.Ratio.html) type.

### `ordered-float`

Adds a dependency on [ordered-float](https://docs.rs/ordered-float) and enables conversions between [ordered-float](https://docs.rs/ordered-float)'s types and Python:

- [NotNan](https://docs.rs/ordered-float/latest/ordered_float/struct.NotNan.html) -> [`PyFloat`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyFloat.html)
- [OrderedFloat](https://docs.rs/ordered-float/latest/ordered_float/struct.OrderedFloat.html) -> [`PyFloat`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyFloat.html)

### `parking-lot`

Adds a dependency on [parking_lot](https://docs.rs/parking_lot) and enables Pyo3's `OnceExt` & `MutexExt` traits for [`parking_lot::Once`](https://docs.rs/parking_lot/latest/parking_lot/struct.Once.html) [`parking_lot::Mutex`](https://docs.rs/parking_lot/latest/parking_lot/type.Mutex.html) and [`parking_lot::ReentrantMutex`](https://docs.rs/parking_lot/latest/parking_lot/type.ReentrantMutex.html) types.

### `rust_decimal`

Adds a dependency on [rust_decimal](https://docs.rs/rust_decimal) and enables conversions into its [`Decimal`](https://docs.rs/rust_decimal/latest/rust_decimal/struct.Decimal.html) type.

### `time`

Adds a dependency on [time](https://docs.rs/time).
Enables conversions between [time](https://docs.rs/time)'s types and Python:

- [Date](https://docs.rs/time/0.3.38/time/struct.Date.html) -> [`PyDate`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDate.html)
- [Time](https://docs.rs/time/0.3.38/time/struct.Time.html) -> [`PyTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyTime.html)
- [OffsetDateTime](https://docs.rs/time/0.3.38/time/struct.OffsetDateTime.html) -> [`PyDateTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDateTime.html)
- [PrimitiveDateTime](https://docs.rs/time/0.3.38/time/struct.PrimitiveDateTime.html) -> [`PyDateTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDateTime.html)
- [Duration](https://docs.rs/time/0.3.38/time/struct.Duration.html) -> [`PyDelta`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDelta.html)
- [UtcOffset](https://docs.rs/time/0.3.38/time/struct.UtcOffset.html) -> [`PyTzInfo`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyTzInfo.html)
- [UtcDateTime](https://docs.rs/time/0.3.38/time/struct.UtcDateTime.html) -> [`PyDateTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDateTime.html)

### `serde`

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

```rust,no_run
# #[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](https://docs.rs/smallvec) and enables conversions into its [`SmallVec`](https://docs.rs/smallvec/latest/smallvec/struct.SmallVec.html) type.

[set-configuration-options]: https://doc.rust-lang.org/reference/conditional-compilation.html#set-configuration-options

### `uuid`

Adds a dependency on [uuid](https://docs.rs/uuid) and enables conversions into its [`Uuid`](https://docs.rs/uuid/latest/uuid/struct.Uuid.html) type.

## Deprecated features for extension module authors

### `extension-module`

Deprecated, users should remove this feature and upgrade to `maturin >= 1.9.4` or `setuptools-rust >= 1.12`.

See the [building and distribution](building-and-distribution.md#the-extension-module-feature) section for further detail.

### `generate-import-lib`

This feature is deprecated and has no effect.
