typing: Attribute.append/prepend (#951)

pynamodb/attributes.py

@@ -13,7 +13,7 @@
 from datetime import timezone
 from inspect import getfullargspec
 from inspect import getmembers
-from typing import Any, Callable, Dict, Generic, List, Mapping, Optional, TypeVar, Type, Union, Set, overload
+from typing import Any, Callable, Dict, Generic, List, Mapping, Optional, TypeVar, Type, Union, Set, overload, Iterable
 from typing import TYPE_CHECKING
 
 from pynamodb._compat import GenericMeta
@@ -198,10 +198,10 @@ def __rsub__(self, other: Any) -> '_Decrement':
     def __or__(self, other: Any) -> '_IfNotExists':
         return Path(self).__or__(other)
 
-    def append(self, other: Any) -> '_ListAppend':
+    def append(self, other: Iterable) -> '_ListAppend':
         return Path(self).append(other)
 
-    def prepend(self, other: Any) -> '_ListAppend':
+    def prepend(self, other: Iterable) -> '_ListAppend':
         return Path(self).prepend(other)
 
     def set(self, value: Any) -> 'SetAction':

tests/test_mypy.py

@@ -227,3 +227,18 @@ class MyModel(Model):
     _ = MyModel.attr.is_in(123)  # E: Argument 1 to "is_in" of "Attribute" has incompatible type "int"; expected "str"  [arg-type]
     _ = MyModel.attr.is_in(['foo', 'bar'])  # E: Argument 1 to "is_in" of "Attribute" has incompatible type "List[str]"; expected "str"  [arg-type]
     """)
+
+
+def test_append(assert_mypy_output):
+    assert_mypy_output("""
+    from pynamodb.models import Model
+    from pynamodb.attributes import ListAttribute, NumberAttribute
+
+    class MyModel(Model):
+        attr = ListAttribute(of=NumberAttribute)
+
+    MyModel.attr.append(42)  # E: Argument 1 to "append" of "Attribute" has incompatible type "int"; expected "Iterable[Any]"  [arg-type]
+    MyModel.attr.append([42])
+    MyModel.attr.prepend(42)  # E: Argument 1 to "prepend" of "Attribute" has incompatible type "int"; expected "Iterable[Any]"  [arg-type]
+    MyModel.attr.prepend([42])
+    """)