fix is_subclass bug where issubclass(list[str], DagsterType) throws a…

… surprising exception (#8287)

python_modules/dagster/dagster/config/field.py

@@ -5,6 +5,7 @@
 from dagster.config.config_schema import ConfigSchemaType
 from dagster.core.errors import DagsterInvalidConfigError, DagsterInvalidDefinitionError
 from dagster.serdes import serialize_value
+from dagster.seven import is_subclass
 from dagster.utils import is_enum_value
 from dagster.utils.typing_api import is_closed_python_optional_type, is_typing_type
 
@@ -13,7 +14,7 @@
 
 
 def _is_config_type_class(obj):
-    return isinstance(obj, type) and issubclass(obj, ConfigType)
+    return isinstance(obj, type) and is_subclass(obj, ConfigType)
 
 
 def helpful_list_error_string():
@@ -111,7 +112,7 @@ def resolve_to_config_type(dagster_type: object) -> Union[ConfigType, bool]:
             'another dagster config type. E.g. "Noneable(Permissive)" should instead be "Noneable(Permissive())".',
         )
 
-    if isinstance(dagster_type, type) and issubclass(dagster_type, DagsterType):
+    if isinstance(dagster_type, type) and is_subclass(dagster_type, DagsterType):
         raise DagsterInvalidDefinitionError(
             "You have passed a DagsterType class {dagster_type} to the config system. "
             "The DagsterType and config schema systems are separate. "

python_modules/dagster/dagster/core/types/dagster_type.py

@@ -15,6 +15,7 @@
 from dagster.core.definitions.metadata import MetadataEntry, RawMetadataValue, normalize_metadata
 from dagster.core.errors import DagsterInvalidDefinitionError, DagsterInvariantViolationError
 from dagster.serdes import whitelist_for_serdes
+from dagster.seven import is_subclass
 
 from ..definitions.resource_requirement import (
     RequiresResources,
@@ -835,12 +836,12 @@ def resolve_dagster_type(dagster_type: object) -> DagsterType:
     from .transform_typing import transform_typing_type
 
     check.invariant(
-        not (isinstance(dagster_type, type) and issubclass(dagster_type, ConfigType)),
+        not is_subclass(dagster_type, ConfigType),
         "Cannot resolve a config type to a runtime type",
     )
 
     check.invariant(
-        not (isinstance(dagster_type, type) and issubclass(dagster_type, DagsterType)),
+        not is_subclass(dagster_type, DagsterType),
         "Do not pass runtime type classes. Got {}".format(dagster_type),
     )
 
@@ -907,12 +908,12 @@ def is_dynamic_output_annotation(dagster_type: object) -> bool:
     from dagster.seven.typing import get_args, get_origin
 
     check.invariant(
-        not (isinstance(dagster_type, type) and issubclass(dagster_type, ConfigType)),
+        not is_subclass(dagster_type, ConfigType),
         "Cannot resolve a config type to a runtime type",
     )
 
     check.invariant(
-        not (isinstance(dagster_type, type) and issubclass(dagster_type, DagsterType)),
+        not is_subclass(dagster_type, DagsterType),
         "Do not pass runtime type classes. Got {}".format(dagster_type),
     )
 

python_modules/dagster/dagster/seven/__init__.py

@@ -168,3 +168,19 @@ def get_import_error_message(import_error):
 @contextmanager
 def nullcontext():
     yield
+
+
+def is_subclass(child_type, parent_type):
+    """Due to some pathological interactions betwen bugs in the Python typing library
+    (https://github.com/python/cpython/issues/88459 and
+    https://github.com/python/cpython/issues/89010), some types (list[str] in Python 3.9, for
+    example) pass inspect.isclass check above but then raise an exception if issubclass is called
+    with the same class. This function provides a workaround for that issue."""
+
+    if not inspect.isclass(child_type):
+        return False
+
+    try:
+        return issubclass(child_type, parent_type)
+    except TypeError:
+        return False

python_modules/dagster/dagster_tests/general_tests/seven_tests/test_seven.py

@@ -1,10 +1,15 @@
+import inspect
 import json
+import sys
 import tempfile
 from functools import update_wrapper
+from typing import List
 
 import pytest
 
-from dagster import seven
+from dagster import DagsterType, seven
+from dagster.core.types.dagster_type import ListType
+from dagster.seven import is_subclass
 from dagster.utils import file_relative_path
 
 
@@ -90,3 +95,37 @@ def yoodles():
     assert seven.is_function_or_decorator_instance_of(bar, Quux) == True
     assert seven.is_function_or_decorator_instance_of(baz, Quux) == False
     assert seven.is_function_or_decorator_instance_of(yoodles, Quux) == True
+
+
+class Foo:
+    pass
+
+
+class Bar(Foo):
+    pass
+
+
+def test_is_subclass():
+    assert is_subclass(Bar, Foo)
+    assert not is_subclass(Foo, Bar)
+
+    assert is_subclass(DagsterType, DagsterType)
+    assert is_subclass(str, str)
+    assert is_subclass(ListType, DagsterType)
+    assert not is_subclass(DagsterType, ListType)
+    assert not is_subclass(ListType, str)
+
+    # type that aren't classes can be passed into is_subclass
+    assert not inspect.isclass(List[str])
+    assert not is_subclass(List[str], DagsterType)
+
+
+@pytest.mark.skipif(
+    sys.version_info.minor < 9, reason="Generic aliases only exist on py39 or later"
+)
+def test_is_subclass_generic_alias():
+    # See comments around is_subclass for why this fails
+    with pytest.raises(TypeError):
+        issubclass(list[str], DagsterType)
+
+    assert not is_subclass(list[str], DagsterType)