--- a/rust/hg-cpython/src/conversion.rs	Sun Dec 02 16:19:22 2018 +0100
+++ b/rust/hg-cpython/src/conversion.rs	Wed Jan 16 16:05:27 2019 +0100
@@ -8,8 +8,12 @@
 //! Bindings for the hg::ancestors module provided by the
 //! `hg-core` crate. From Python, this will be seen as `rustext.ancestor`
 
-use cpython::{ObjectProtocol, PyObject, PyResult, Python};
+use cpython::{
+    ObjectProtocol, PyDict, PyObject, PyResult, PyTuple, Python, PythonObject,
+    ToPyObject,
+};
 use hg::Revision;
+use std::collections::HashSet;
 use std::iter::FromIterator;
 
 /// Utility function to convert a Python iterable into various collections
@@ -26,3 +30,21 @@
         .map(|r| r.and_then(|o| o.extract::<Revision>(py)))
         .collect()
 }
+
+/// Copy and convert an `HashSet<Revision>` in a Python set
+///
+/// This will probably turn useless once `PySet` support lands in
+/// `rust-cpython`.
+///
+/// This builds a Python tuple, then calls Python's "set()" on it
+pub fn py_set(py: Python, set: &HashSet<Revision>) -> PyResult<PyObject> {
+    let as_vec: Vec<PyObject> = set
+        .iter()
+        .map(|rev| rev.to_py_object(py).into_object())
+        .collect();
+    let as_pytuple = PyTuple::new(py, as_vec.as_slice());
+
+    let locals = PyDict::new(py);
+    locals.set_item(py, "obj", as_pytuple.to_py_object(py))?;
+    py.eval("set(obj)", None, Some(&locals))
+}