Allow #[pymethods] to use lifetime

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
  * PyPy support by omerbenamram in [#393](https://github.com/PyO3/pyo3/pull/393)
  * Have `PyModule` generate an index of its members (`__all__` list).
  * Allow `slf: PyRef<T>` for pyclass(#419)
+ * Allow to use lifetime specifiers in `pymethods`
  * Add `marshal` module. [#460](https://github.com/PyO3/pyo3/pull/460)
 
 ### Changed

pyo3-derive-backend/src/pymethod.rs

@@ -40,8 +40,18 @@ pub fn gen_py_method(
 }
 
 fn check_generic(name: &syn::Ident, sig: &syn::MethodSig) {
-    if !sig.decl.generics.params.is_empty() {
-        panic!("python method can not be generic: {:?}", name);
+    for param in &sig.decl.generics.params {
+        match param {
+            syn::GenericParam::Lifetime(_) => {}
+            syn::GenericParam::Type(_) => panic!(
+                "A Python method can't have a generic type parameter: {}",
+                name
+            ),
+            syn::GenericParam::Const(_) => panic!(
+                "A Python method can't have a const generic parameter: {}",
+                name
+            ),
+        }
     }
 }
 

tests/test_methods.rs

@@ -1,5 +1,5 @@
 use pyo3::prelude::*;
-use pyo3::types::{IntoPyDict, PyDict, PyString, PyTuple, PyType};
+use pyo3::types::{IntoPyDict, PyDict, PyList, PySet, PyString, PyTuple, PyType};
 use pyo3::PyRawObject;
 
 #[macro_use]
@@ -306,3 +306,31 @@ fn meth_doc() {
     )
     .unwrap();
 }
+
+#[pyclass]
+struct MethodWithLifeTime {}
+
+#[pymethods]
+impl MethodWithLifeTime {
+    fn set_to_list<'py>(&self, py: Python<'py>, set: &'py PySet) -> PyResult<&'py PyList> {
+        let mut items = vec![];
+        for _ in 0..set.len() {
+            items.push(set.pop().unwrap());
+        }
+        let list = PyList::new(py, items);
+        list.sort()?;
+        Ok(list)
+    }
+}
+
+#[test]
+fn method_with_lifetime() {
+    let gil = Python::acquire_gil();
+    let py = gil.python();
+    let obj = PyRef::new(py, MethodWithLifeTime {}).unwrap();
+    py_run!(
+        py,
+        obj,
+        "assert obj.set_to_list(set((1, 2, 3))) == [1, 2, 3]"
+    );
+}