Handle older Python versions

Author: mciszczon

dacite/core.py

@@ -1,6 +1,11 @@
 from dataclasses import is_dataclass
 from itertools import zip_longest
-from typing import TypeVar, Type, Optional, get_type_hints, Mapping, Any, Collection, MutableMapping, get_origin
+from typing import TypeVar, Type, Optional, get_type_hints, Mapping, Any, Collection, MutableMapping
+
+try:
+    from typing import get_origin
+except ImportError:
+    from typing_extensions import get_origin
 
 from dacite.cache import cache
 from dacite.config import Config
@@ -99,7 +104,9 @@ def _build_value(type_: Type, data: Any, config: Config) -> Any:
     elif cache(is_dataclass)(type_) and isinstance(data, Mapping):
         data = from_dict(data_class=type_, data=data, config=config)
     elif is_generic_subclass(type_) and is_dataclass(get_origin(type_)):
-        data = from_dict(data_class=get_origin(type_), data=data, config=config)
+        origin = get_origin(type_)
+        assert origin is not None
+        data = from_dict(data_class=origin, data=data, config=config)
     for cast_type in config.cast:
         if is_subclass(type_, cast_type):
             if is_generic_collection(type_):

dacite/types.py

@@ -1,19 +1,10 @@
 from dataclasses import InitVar
-from typing import (
-    Type,
-    Any,
-    Optional,
-    Union,
-    Collection,
-    TypeVar,
-    Mapping,
-    Tuple,
-    get_origin,
-    get_type_hints,
-    get_args,
-    cast as typing_cast,
-    _GenericAlias,  # Remove import and check for Generic in a different way
-)
+from typing import Type, Any, Optional, Union, Collection, TypeVar, Mapping, Tuple, get_type_hints, cast as typing_cast
+
+try:
+    from typing import get_origin, get_args
+except ImportError:
+    from typing_extensions import get_origin, get_args
 from inspect import isclass
 
 from dacite.cache import cache
@@ -53,14 +44,9 @@ def is_generic_subclass(type_: Type) -> bool:
     return is_generic(type_) and hasattr(type_, "__args__")
 
 
-@cache
-def is_generic_alias(type_: Type) -> bool:
-    return type(type_.__args__) == _GenericAlias
-
-
 @cache
 def is_union(type_: Type) -> bool:
-    if is_generic(type_) and type_.__origin__ == Union:
+    if is_generic(type_) and get_origin(type_) == Union:
         return True
 
     try:
@@ -81,7 +67,7 @@ def is_literal(type_: Type) -> bool:
     try:
         from typing import Literal  # type: ignore
 
-        return is_generic(type_) and type_.__origin__ == Literal
+        return is_generic(type_) and get_origin(type_) == Literal
     except ImportError:
         return False
 
@@ -101,10 +87,22 @@ def is_init_var(type_: Type) -> bool:
     return isinstance(type_, InitVar) or type_ is InitVar
 
 
+@cache
+def is_generic_alias(type_: Type) -> bool:
+    """Since `typing._GenericAlias` is not explicitly exported, we instead rely on this check."""
+    return str(type_) == "<class 'typing._GenericAlias'>"
+
+
+@cache
+def has_generic_alias_in_args(type_: Type) -> bool:
+    return is_generic_alias(type(get_args(type_)))
+
+
 def is_valid_generic_class(value: Any, type_: Type) -> bool:
-    if not isinstance(value, get_origin(type_)):
+    origin = get_origin(type_)
+    if not (origin and isinstance(value, origin)):
         return False
-    type_hints = get_type_hints(value)
+    type_hints = get_type_hints(type(value))
     for field_name, field_type in type_hints.items():
         if isinstance(field_type, TypeVar):
             return (
@@ -165,7 +163,7 @@ def is_instance(value: Any, type_: Type) -> bool:
         return value in extract_generic(type_)
     elif is_init_var(type_):
         return is_instance(value, extract_init_var(type_))
-    elif isclass(type(type_)) and type(type_) == _GenericAlias:
+    elif isclass(type(type_)) and is_generic_alias(type(type_)):
         return is_valid_generic_class(value, type_)
     elif isinstance(type_, TypeVar):
         if hasattr(type_, "__constraints__") and type_.__constraints__:
@@ -174,7 +172,7 @@ def is_instance(value: Any, type_: Type) -> bool:
             if isinstance(type_.__bound__, tuple):
                 return any(is_instance(value, t) for t in type_.__bound__)
             if type_.__bound__ is not None and is_generic(type_.__bound__):
-                return isinstance(value, type_.__bound__)
+                return isinstance(value, extract_generic(type_.__bound__))
         return True
     elif is_type_generic(type_):
         return is_subclass(value, extract_generic(type_)[0])
@@ -218,6 +216,6 @@ def is_subclass(sub_type: Type, base_type: Type) -> bool:
 @cache
 def is_type_generic(type_: Type) -> bool:
     try:
-        return type_.__origin__ in (type, Type)
+        return get_origin(type_) in (type, Type)
     except AttributeError:
         return False

tests/core/test_base.py

@@ -193,7 +193,7 @@ class X:
     assert result == X(s=MyStr("test"))
 
 
-def test_from_dict_generic():
+def test_from_dict_generic_valid():
     T = TypeVar("T", bound=Union[str, int])
 
     @dataclass