datasette.utils.check_callable(obj) - refs #2078

datasette/utils/callable.py

@@ -0,0 +1,25 @@
+import asyncio
+import types
+from typing import NamedTuple, Any
+
+
+class CallableStatus(NamedTuple):
+    is_callable: bool
+    is_async_callable: bool
+
+
+def check_callable(obj: Any) -> CallableStatus:
+    if not callable(obj):
+        return CallableStatus(False, False)
+
+    if isinstance(obj, type):
+        # It's a class
+        return CallableStatus(True, False)
+
+    if isinstance(obj, types.FunctionType):
+        return CallableStatus(True, asyncio.iscoroutinefunction(obj))
+
+    if hasattr(obj, "__call__"):
+        return CallableStatus(True, asyncio.iscoroutinefunction(obj.__call__))
+
+    assert False, "obj {} is somehow callable with no __call__ method".format(repr(obj))

tests/test_utils_callable.py

@@ -0,0 +1,46 @@
+from datasette.utils.callable import check_callable
+import pytest
+
+
+class AsyncClass:
+    async def __call__(self):
+        pass
+
+
+class NotAsyncClass:
+    def __call__(self):
+        pass
+
+
+class ClassNoCall:
+    pass
+
+
+async def async_func():
+    pass
+
+
+def non_async_func():
+    pass
+
+
+@pytest.mark.parametrize(
+    "obj,expected_is_callable,expected_is_async_callable",
+    (
+        (async_func, True, True),
+        (non_async_func, True, False),
+        (AsyncClass(), True, True),
+        (NotAsyncClass(), True, False),
+        (ClassNoCall(), False, False),
+        (AsyncClass, True, False),
+        (NotAsyncClass, True, False),
+        (ClassNoCall, True, False),
+        ("", False, False),
+        (1, False, False),
+        (str, True, False),
+    ),
+)
+def test_check_callable(obj, expected_is_callable, expected_is_async_callable):
+    status = check_callable(obj)
+    assert status.is_callable == expected_is_callable
+    assert status.is_async_callable == expected_is_async_callable