From 3965d1a026d956659a309e569c254c081ebcb285 Mon Sep 17 00:00:00 2001
From: Adam Reichold <adam.reichold@t-online.de>
Date: Sun, 3 Apr 2022 09:30:26 +0200
Subject: [PATCH] Add PyString::intern to enable access to Python's built-in
 string interning.

---
 CHANGELOG.md        |  1 +
 src/types/string.rs | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index db19eba9431..6a95190576a 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 `PyString::intern` to enable usage of the Python's built-in string interning. [#2268](https://github.com/PyO3/pyo3/pull/2268)
 
 ### Changed
 
diff --git a/src/types/string.rs b/src/types/string.rs
index 76610a108ae..4e906f8ce51 100644
--- a/src/types/string.rs
+++ b/src/types/string.rs
@@ -144,6 +144,26 @@ impl PyString {
         unsafe { py.from_owned_ptr(ffi::PyUnicode_FromStringAndSize(ptr, len)) }
     }
 
+    /// Intern the given string
+    ///
+    /// This will return a reference to the same Python string object if called repeatedly with the same string.
+    ///
+    /// Note that while this is more memory efficient than [`PyString::new`], it unconditionally allocates a
+    /// temporary Python string object and is thereby slower than [`PyString::new`].
+    ///
+    /// Panics if out of memory.
+    pub fn intern<'p>(py: Python<'p>, s: &str) -> &'p PyString {
+        let ptr = s.as_ptr() as *const c_char;
+        let len = s.len() as ffi::Py_ssize_t;
+        unsafe {
+            let mut ob = ffi::PyUnicode_FromStringAndSize(ptr, len);
+            if !ob.is_null() {
+                ffi::PyUnicode_InternInPlace(&mut ob);
+            }
+            py.from_owned_ptr(ob)
+        }
+    }
+
     /// Attempts to create a Python string from a Python [bytes-like object].
     ///
     /// [bytes-like object]: (https://docs.python.org/3/glossary.html#term-bytes-like-object).
@@ -592,4 +612,22 @@ mod tests {
             assert_eq!(data.to_string_lossy(), Cow::Owned::<str>("𠀀�".into()));
         });
     }
+
+    #[test]
+    fn test_intern_string() {
+        Python::with_gil(|py| {
+            let py_string1 = PyString::intern(py, "foo");
+            assert_eq!(py_string1.to_str().unwrap(), "foo");
+
+            let py_string2 = PyString::intern(py, "foo");
+            assert_eq!(py_string2.to_str().unwrap(), "foo");
+
+            assert_eq!(py_string1.as_ptr(), py_string2.as_ptr());
+
+            let py_string3 = PyString::intern(py, "bar");
+            assert_eq!(py_string3.to_str().unwrap(), "bar");
+
+            assert_ne!(py_string1.as_ptr(), py_string3.as_ptr());
+        });
+    }
 }