Fix callable protocols (#599)

CHANGELOG.rst

@@ -33,6 +33,8 @@ Fixed
   <https://github.com/omni-us/jsonargparse/pull/608>`__).
 - Failure when resolving forward references from dataclass parameter types
   (`#611 <https://github.com/omni-us/jsonargparse/pull/611>`__).
+- Fix callable protocol inheritance.
+  (`#599 <https://github.com/omni-us/jsonargparse/pull/599>`__).
 
 Changed
 ^^^^^^^

jsonargparse/_typehints.py

@@ -1087,15 +1087,32 @@ def adapt_typehints(
     return val
 
 
+protocol_irrelevant_dunder_methods = {
+    "__init__",
+    "__new__",
+    "__del__",
+    "__getattr__",
+    "__getattribute__",
+    "__setattr__",
+    "__delattr__",
+    "__reduce__",
+    "__reduce_ex__",
+    "__getstate__",
+    "__setstate__",
+    "__subclasshook__",
+}
+
+
 def implements_protocol(value, protocol) -> bool:
     from jsonargparse._parameter_resolvers import get_signature_parameters
     from jsonargparse._postponed_annotations import get_return_type
 
-    if not inspect.isclass(value):
+    if not inspect.isclass(value) or value is object:
         return False
     members = 0
     for name, _ in inspect.getmembers(protocol, predicate=inspect.isfunction):
-        if name.startswith("_"):
+        is_dunder = name.startswith("__") and name.endswith("__")
+        if (not is_dunder and name.startswith("_")) or (is_dunder and name in protocol_irrelevant_dunder_methods):
             continue
         if not hasattr(value, name):
             return False

jsonargparse_tests/test_subclasses.py

@@ -1500,6 +1500,51 @@ def test_parse_implements_protocol(parser):
     ctx.match("Not a valid subclass of Interface")
 
 
+# callable protocol tests
+
+
+class CallableInterface(Protocol):
+    def __call__(self, items: List[float]) -> List[float]: ...
+
+
+class ImplementsCallableInterface1:
+    def __init__(self, batch_size: int):
+        self.batch_size = batch_size
+
+    def __call__(self, items: List[float]) -> List[float]:
+        return items
+
+
+class NotImplementsCallableInterface1:
+    def __call__(self, items: str) -> List[float]:
+        return []
+
+
+class NotImplementsCallableInterface2:
+    def __call__(self, items: List[float], extra: int) -> List[float]:
+        return items
+
+
+class NotImplementsCallableInterface3:
+    def __call__(self, items: List[float]) -> None:
+        return
+
+
+@pytest.mark.parametrize(
+    "expected, value",
+    [
+        (True, ImplementsCallableInterface1),
+        (False, ImplementsCallableInterface1(1)),
+        (False, NotImplementsCallableInterface1),
+        (False, NotImplementsCallableInterface2),
+        (False, NotImplementsCallableInterface3),
+        (False, object),
+    ],
+)
+def test_implements_callable_protocol(expected, value):
+    assert implements_protocol(value, CallableInterface) is expected
+
+
 # parameter skip tests