Pass only relevant validate kwargs to Optional(default=...)

schema.py

@@ -2,8 +2,8 @@
 obtained from config-files, forms, external services or command-line
 parsing, converted from JSON/YAML (or something else) to Python data-types."""
 
-import inspect
 import re
+from inspect import signature
 
 try:
     from contextlib import ExitStack
@@ -273,11 +273,20 @@ def _priority(s):
         return COMPARABLE
 
 
-def _invoke_with_optional_kwargs(f, **kwargs):
-    s = inspect.signature(f)
-    if len(s.parameters) == 0:
+def _invoke_with_relevant_kwargs(f, **kwargs):
+    try:
+        sig = signature(f)
+    except ValueError as e:
+        if e.args[0].startswith("no signature found for builtin type"):
+            builtin = True
+        else:
+            raise
+    else:
+        builtin = False
+    if builtin:
         return f()
-    return f(**kwargs)
+    relevant_param_names = set(sig.parameters.keys()) & set(kwargs.keys())
+    return f(**{name: kwargs[name] for name in relevant_param_names})
 
 
 class Schema(object):
@@ -428,7 +437,11 @@ def validate(self, data, **kwargs):
             # Apply default-having optionals that haven't been used:
             defaults = set(k for k in s if isinstance(k, Optional) and hasattr(k, "default")) - coverage
             for default in defaults:
-                new[default.key] = _invoke_with_optional_kwargs(default.default, **kwargs) if callable(default.default) else default.default
+                new[default.key] = (
+                    _invoke_with_relevant_kwargs(default.default, **kwargs)
+                    if callable(default.default)
+                    else default.default
+                )
 
             return new
         if flavor == TYPE:
@@ -659,7 +672,11 @@ def _get_key_name(key):
                                 sub_schema, is_main_schema=False, description=_get_key_description(key)
                             )
                             if isinstance(key, Optional) and hasattr(key, "default"):
-                                expanded_schema[key_name]["default"] = _to_json_type(_invoke_with_optional_kwargs(key.default, **kwargs) if callable(key.default) else key.default)
+                                expanded_schema[key_name]["default"] = _to_json_type(
+                                    _invoke_with_relevant_kwargs(key.default, **kwargs)
+                                    if callable(key.default)
+                                    else key.default
+                                )
                         elif isinstance(key_name, Or):
                             # JSON schema does not support having a key named one name or another, so we just add both options
                             # This is less strict because we cannot enforce that one or the other is required

test_schema.py

@@ -747,7 +747,7 @@ def convert(data, increment):
             return data + increment
         return data
 
-    s = {"k": int, "d": {Optional("k", default=lambda **kw: convert(2, kw['increment'])): int, "l": [{"l": [int]}]}}
+    s = {"k": int, "d": {Optional("k", default=lambda increment: convert(2, increment)): int, "l": [{"l": [int]}]}}
     v = {"k": 1, "d": {"l": [{"l": [3, 4, 5]}]}}
     d = Schema(s).validate(v, increment=1)
     assert d["k"] == 1 and d["d"]["k"] == 3 and d["d"]["l"][0]["l"] == [3, 4, 5]
@@ -783,12 +783,7 @@ class MyOptional(Optional):
         """
         @property
         def default(self):
-
-            def wrapper(**kwargs):
-                if 'increment' in kwargs:
-                    return convert(self._default, kwargs['increment'])
-                return self._default
-            return wrapper
+            return lambda increment: convert(self._default, increment)
 
         @default.setter
         def default(self, value):
@@ -1125,9 +1120,7 @@ def default_func():
 
 
 def test_json_schema_default_is_callable_with_args_passed_from_json_schema():
-    def default_func(**kwargs):
-        return 'Hello, ' + kwargs['name']
-    s = Schema({Optional("test", default=default_func): str})
+    s = Schema({Optional("test", default=lambda name: "Hello, " + name): str})
     assert s.json_schema("my-id", name='World!') == {
         "$schema": "http://json-schema.org/draft-07/schema#",
         "$id": "my-id",