Add PyString::intern to enable access to Python's built-in string interning.

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
 

pyo3-macros-backend/src/pyimpl.rs

@@ -88,7 +88,7 @@ pub fn build_py_methods(
 
 pub fn impl_methods(
     ty: &syn::Type,
-    impls: &mut Vec<syn::ImplItem>,
+    impls: &mut [syn::ImplItem],
     methods_type: PyClassMethodsType,
     options: PyImplOptions,
 ) -> syn::Result<TokenStream> {

pyo3-macros-backend/src/pyproto.rs

@@ -44,7 +44,7 @@ pub fn build_py_proto(ast: &mut syn::ItemImpl) -> syn::Result<TokenStream> {
 
 fn impl_proto_impl(
     ty: &syn::Type,
-    impls: &mut Vec<syn::ImplItem>,
+    impls: &mut [syn::ImplItem],
     proto: &defs::Proto,
 ) -> syn::Result<TokenStream> {
     let mut trait_impls = TokenStream::new();

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());
+        });
+    }
 }