improve performance for noncallble attributes (#8502)

Co-authored-by: Dima Kryukov <dmitry.kryukov@pandadoc.com>

rest_framework/fields.py

@@ -62,6 +62,9 @@ def is_simple_callable(obj):
     """
     True if the object is a callable that takes no arguments.
     """
+    if not callable(obj):
+        return False
+
     # Bail early since we cannot inspect built-in function signatures.
     if inspect.isbuiltin(obj):
         raise BuiltinSignatureError(

tests/test_fields.py

@@ -75,6 +75,10 @@ class TestIsSimpleCallable:
         assert is_simple_callable(valid_vargs_kwargs)
         assert not is_simple_callable(invalid)
 
+    @pytest.mark.parametrize('obj', (True, None, "str", b'bytes', 123, 1.23))
+    def test_not_callable(self, obj):
+        assert not is_simple_callable(obj)
+
     def test_4602_regression(self):
         from django.db import models