Fix passing explicit None to pyfunction with default

CHANGELOG.md

@@ -8,6 +8,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Removed
 - Remove `ManagedPyRef` (unused, and needs specialization) [#930](https://github.com/PyO3/pyo3/pull/930)
 
+### Fixed
+- Fix passing explicit `None` to `Option<T>` argument `#[pyfunction]` with a default value. [#936](https://github.com/PyO3/pyo3/pull/936)
+
 ## [0.10.1] - 2020-05-14
 ### Fixed
 - Fix deadlock in `Python::acquire_gil()` after dropping a `PyObject` or `Py<T>`. [#924](https://github.com/PyO3/pyo3/pull/924)

pyo3-derive-backend/src/pymethod.rs

@@ -520,9 +520,9 @@ fn impl_arg_param(
             };
             // Get Option<&T> from Option<PyRef<T>>
             quote! {
-                let #mut_ _tmp = match #arg_value.as_ref().filter(|obj| !obj.is_none()) {
+                let #mut_ _tmp = match #arg_value {
                     Some(_obj) => {
-                        Some(_obj.extract::<<#tref as pyo3::derive_utils::ExtractExt>::Target>()?)
+                        _obj.extract::<Option<<#tref as pyo3::derive_utils::ExtractExt>::Target>>()?
                     },
                     None => #default,
                 };
@@ -530,15 +530,15 @@ fn impl_arg_param(
             }
         } else {
             quote! {
-                let #arg_name = match #arg_value.as_ref().filter(|obj| !obj.is_none()) {
-                    Some(_obj) => Some(_obj.extract()?),
+                let #arg_name = match #arg_value {
+                    Some(_obj) => _obj.extract()?,
                     None => #default,
                 };
             }
         }
     } else if let Some(default) = spec.default_value(name) {
         quote! {
-            let #arg_name = match #arg_value.as_ref().filter(|obj| !obj.is_none()) {
+            let #arg_name = match #arg_value {
                 Some(_obj) => _obj.extract()?,
                 None => #default,
             };

tests/test_pyfunction.rs

@@ -0,0 +1,22 @@
+use pyo3::prelude::*;
+use pyo3::wrap_pyfunction;
+
+mod common;
+
+#[pyfunction(arg = "true")]
+fn optional_bool(arg: Option<bool>) -> String {
+    format!("{:?}", arg)
+}
+
+#[test]
+fn test_optional_bool() {
+    // Regression test for issue #932
+    let gil = Python::acquire_gil();
+    let py = gil.python();
+    let f = wrap_pyfunction!(optional_bool)(py);
+
+    py_assert!(py, f, "f() == 'Some(true)'");
+    py_assert!(py, f, "f(True) == 'Some(true)'");
+    py_assert!(py, f, "f(False) == 'Some(false)'");
+    py_assert!(py, f, "f(None) == 'None'");
+}