diff --git a/rust/hg-cpython/src/ancestors.rs b/rust/hg-cpython/src/ancestors.rs
--- a/rust/hg-cpython/src/ancestors.rs
+++ b/rust/hg-cpython/src/ancestors.rs
@@ -34,11 +34,11 @@
 //! [`LazyAncestors`]: struct.LazyAncestors.html
 //! [`MissingAncestors`]: struct.MissingAncestors.html
 //! [`AncestorsIterator`]: struct.AncestorsIterator.html
-use crate::conversion::rev_pyiter_collect;
+use crate::conversion::{py_set, rev_pyiter_collect};
 use cindex::Index;
 use cpython::{
     ObjectProtocol, PyClone, PyDict, PyList, PyModule, PyObject, PyResult,
-    PyTuple, Python, PythonObject, ToPyObject,
+    Python, PythonObject, ToPyObject,
 };
 use exceptions::GraphError;
 use hg::Revision;
@@ -90,24 +90,6 @@ impl AncestorsIterator {
     }
 }
 
-/// 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
-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))
-}
-
 py_class!(pub class LazyAncestors |py| {
     data inner: RefCell<Box<CoreLazy<Index>>>;
 
diff --git a/rust/hg-cpython/src/conversion.rs b/rust/hg-cpython/src/conversion.rs
--- a/rust/hg-cpython/src/conversion.rs
+++ b/rust/hg-cpython/src/conversion.rs
@@ -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 @@ where
         .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))
+}