From a4629d76aab32ee26c0003589f0914077ce67f5c Mon Sep 17 00:00:00 2001
From: Adam Reichold <adam.reichold@t-online.de>
Date: Sun, 3 Apr 2022 12:27:34 +0200
Subject: [PATCH] Add intern! macro which can be used to amortize the cost of
 creating Python objects by storing them inside a GILOnceCell.

---
 CHANGELOG.md     |  1 +
 src/lib.rs       |  1 +
 src/once_cell.rs | 43 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 45 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index db19eba9431..453363f21be 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Allow dependent crates to access config values from `pyo3-build-config` via cargo link dep env vars. [#2092](https://github.com/PyO3/pyo3/pull/2092)
 - Added methods on `InterpreterConfig` to run Python scripts using the configured executable. [#2092](https://github.com/PyO3/pyo3/pull/2092)
 - Added FFI definitions for `PyType_FromModuleAndSpec`, `PyType_GetModule`, `PyType_GetModuleState` and `PyModule_AddType`. [#2250](https://github.com/PyO3/pyo3/pull/2250)
+- Add `intern!` macro which can be used to amortize the cost of creating Python objects by storing them inside a `GILOnceCell`. [#2269](https://github.com/PyO3/pyo3/pull/2269)
 
 ### Changed
 
diff --git a/src/lib.rs b/src/lib.rs
index ce2a1e24905..6da166235c7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -375,6 +375,7 @@ pub mod impl_;
 mod instance;
 pub mod marker;
 pub mod marshal;
+#[macro_use]
 pub mod once_cell;
 pub mod panic;
 pub mod prelude;
diff --git a/src/once_cell.rs b/src/once_cell.rs
index 739864c5ab0..4e835ba4752 100644
--- a/src/once_cell.rs
+++ b/src/once_cell.rs
@@ -101,3 +101,46 @@ impl<T> GILOnceCell<T> {
         Ok(())
     }
 }
+
+/// Converts `value` into a Python object and stores it in static storage. The same Python object
+/// is returned on each invocation.
+///
+/// Because it is stored in a static, this object's destructor will not run.
+///
+/// # Example: Using `intern!` to avoid needlessly recreating the same object
+///
+/// ```
+/// use pyo3::intern;
+/// # use pyo3::{pyfunction, types::PyDict, PyResult, Python};
+///
+/// #[pyfunction]
+/// fn create_dict(py: Python<'_>) -> PyResult<&PyDict> {
+///    let dict = PyDict::new(py);
+///    //             👇 A new `PyString` is created
+///    //                for every call of this function
+///    dict.set_item("foo", 42)?;
+///    Ok(dict)
+/// }
+///
+/// #[pyfunction]
+/// fn create_dict_faster(py: Python<'_>) -> PyResult<&PyDict> {
+///    let dict = PyDict::new(py);
+///    //               👇 A `PyString` is created once and reused
+///    //                  for the lifetime of the program.
+///    dict.set_item(intern!(py, "foo"), 42)?;
+///    Ok(dict)
+/// }
+/// ```
+#[macro_export]
+macro_rules! intern {
+    ($py: expr, $value: expr) => {{
+        static INTERNED: $crate::once_cell::GILOnceCell<$crate::PyObject> =
+            $crate::once_cell::GILOnceCell::new();
+
+        INTERNED
+            .get_or_init($py, || {
+                $crate::conversion::ToPyObject::to_object($value, $py)
+            })
+            .as_ref($py)
+    }};
+}