Add support for __await__, __aiter__, and __anext__ protocols (#1842)

include/pybind11/detail/class.h

@@ -586,6 +586,9 @@ inline PyObject* make_new_python_type(const type_record &rec) {
     type->tp_as_number = &heap_type->as_number;
     type->tp_as_sequence = &heap_type->as_sequence;
     type->tp_as_mapping = &heap_type->as_mapping;
+#if PY_VERSION_HEX >= 0x03050000
+    type->tp_as_async = &heap_type->as_async;
+#endif
 
     /* Flags */
     type->tp_flags |= Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HEAPTYPE;

tests/CMakeLists.txt

@@ -26,6 +26,7 @@ endif()
 
 # Full set of test files (you can override these; see below)
 set(PYBIND11_TEST_FILES
+  test_async.cpp
   test_buffers.cpp
   test_builtin_casters.cpp
   test_call_policies.cpp
@@ -71,6 +72,13 @@ if (PYBIND11_TEST_OVERRIDE)
   set(PYBIND11_TEST_FILES ${PYBIND11_TEST_OVERRIDE})
 endif()
 
+# Skip test_async for Python < 3.5
+list(FIND PYBIND11_TEST_FILES test_async.cpp PYBIND11_TEST_FILES_ASYNC_I)
+if((PYBIND11_TEST_FILES_ASYNC_I GREATER -1) AND ("${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR}" VERSION_LESS 3.5))
+  message(STATUS "Skipping test_async because Python version ${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR} < 3.5")
+  list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_ASYNC_I})
+endif()
+
 string(REPLACE ".cpp" ".py" PYBIND11_PYTEST_FILES "${PYBIND11_TEST_FILES}")
 
 # Contains the set of test files that require pybind11_cross_module_tests to be

tests/conftest.py

@@ -17,6 +17,11 @@ _unicode_marker = re.compile(r'u(\'[^\']*\')')
 _long_marker = re.compile(r'([0-9])L')
 _hexadecimal = re.compile(r'0x[0-9a-fA-F]+')
 
+# test_async.py requires support for async and await
+collect_ignore = []
+if sys.version_info[:2] < (3, 5):
+    collect_ignore.append("test_async.py")
+
 
 def _strip_and_dedent(s):
     """For triple-quote strings"""

tests/test_async.cpp

+/*
+    tests/test_async.cpp -- __await__ support
+
+    Copyright (c) 2019 Google Inc.
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#include "pybind11_tests.h"
+
+TEST_SUBMODULE(async_module, m) {
+    struct DoesNotSupportAsync {};
+    py::class_<DoesNotSupportAsync>(m, "DoesNotSupportAsync")
+        .def(py::init<>());
+    struct SupportsAsync {};
+    py::class_<SupportsAsync>(m, "SupportsAsync")
+        .def(py::init<>())
+        .def("__await__", [](const SupportsAsync& self) -> py::object {
+            static_cast<void>(self);
+            py::object loop = py::module::import("asyncio.events").attr("get_event_loop")();
+            py::object f = loop.attr("create_future")();
+            f.attr("set_result")(5);
+            return f.attr("__await__")();
+        });
+}

tests/test_async.py

+import asyncio
+import pytest
+from pybind11_tests import async_module as m
+
+
+@pytest.fixture
+def event_loop():
+    loop = asyncio.new_event_loop()
+    yield loop
+    loop.close()
+
+
+async def get_await_result(x):
+    return await x
+
+
+def test_await(event_loop):
+    assert 5 == event_loop.run_until_complete(get_await_result(m.SupportsAsync()))
+
+
+def test_await_missing(event_loop):
+    with pytest.raises(TypeError):
+        event_loop.run_until_complete(get_await_result(m.DoesNotSupportAsync()))