Support removing specific indexes from a ListAttribute (#754)

Author: dotpmrcunha

docs/updates.rst

@@ -44,4 +44,5 @@ Any value provided will be serialized using the serializer defined for that attr
     `attr_or_value_1` \- `attr_or_value_2`, `attr_or_value_1` \- `attr_or_value_2`, 5 - Thread.views
     "list_append( `attr` , `value` )", append( `value` ), Thread.notes.append(['my last note'])
     "list_append( `value` , `attr` )", prepend( `value` ), Thread.notes.prepend(['my first note'])
+    "REMOVE list[index1], list[index2]", "remove_indexes(`index1`, `index2`)", "Thread.notes.remove_indexes(0, 1)"
     "if_not_exists( `attr`, `value` )", `attr` | `value`, Thread.forum_name | 'Default Forum Name'

pynamodb/attributes.py

@@ -961,6 +961,11 @@ def __init__(self, hash_key=False, range_key=False, null=None, default=None, att
                 raise ValueError("'of' must be subclass of MapAttribute")
             self.element_type = of
 
+    def remove_indexes(self, *indexes):
+        if not all([isinstance(i, int) for i in indexes]):
+            raise ValueError("Method 'remove_indexes' arguments must be 'int'")
+        return Path(self).remove_list_elements(*indexes)
+
     def serialize(self, values):
         """
         Encode the given list of objects into a list of AttributeValue types.

pynamodb/attributes.pyi

@@ -9,7 +9,7 @@ from pynamodb.expressions.operand import (
     _Decrement, _IfNotExists, _Increment, _ListAppend
 )
 from pynamodb.expressions.update import (
-    AddAction, DeleteAction, RemoveAction, SetAction
+    AddAction, DeleteAction, RemoveAction, SetAction, ListRemoveAction
 )
 
 
@@ -168,6 +168,8 @@ class ListAttribute(Generic[_T], Attribute[List[_T]]):
     def __get__(self: _A, instance: None, owner: Any) -> _A: ...
     @overload
     def __get__(self, instance: Any, owner: Any) -> List[_T]: ...
+    def remove_indexes(self, *indexes: int) -> Union[ListRemoveAction]: ...
+
 
 DESERIALIZE_CLASS_MAP: Dict[Text, Attribute]
 SERIALIZE_CLASS_MAP: Dict[Type, Attribute]

pynamodb/expressions/operand.py

@@ -6,7 +6,7 @@
     BeginsWith, Between, Comparison, Contains, Exists, In, IsType, NotExists
 )
 from pynamodb.expressions.update import (
-    AddAction, DeleteAction, RemoveAction, SetAction
+    AddAction, DeleteAction, RemoveAction, SetAction, ListRemoveAction
 )
 from pynamodb.expressions.util import get_path_segments, get_value_placeholder, substitute_names
 from six import string_types
@@ -277,6 +277,9 @@ def remove(self):
         # Returns an update action that removes this attribute from the item
         return RemoveAction(self)
 
+    def remove_list_elements(self, *indexes):
+        return ListRemoveAction(self, *indexes)
+
     def add(self, *values):
         # Returns an update action that appends the given values to a set or mathematically adds a value to a number
         value = values[0] if len(values) == 1 else values

pynamodb/expressions/operand.pyi

@@ -5,7 +5,7 @@ from pynamodb.expressions.condition import (
     BeginsWith, Between, Comparison, Contains, Exists, In, IsType, NotExists
 )
 from pynamodb.expressions.update import (
-    AddAction, DeleteAction, RemoveAction, SetAction
+    AddAction, DeleteAction, RemoveAction, SetAction, ListRemoveAction
 )
 
 
@@ -78,3 +78,4 @@ class Path(_NumericOperand, _ListAppendOperand, _ConditionOperand):
     def contains(self, item: Any) -> Contains: ...
     def set(self, value: Any) -> SetAction: ...
     def remove(self) -> RemoveAction: ...
+    def remove_list_elements(self, *indexes: int) -> ListRemoveAction: ...

pynamodb/expressions/update.py

@@ -36,6 +36,17 @@ def __init__(self, path):
         super(RemoveAction, self).__init__(path)
 
 
+class ListRemoveAction(Action):
+    """
+    The List REMOVE action deletes an element from a list item based on the index.
+    """
+    format_string = None
+
+    def __init__(self, path, *indexes):
+        self.format_string = ", ".join("{{0}}[{}]".format(index) for index in indexes)
+        super(ListRemoveAction, self).__init__(path)
+
+
 class AddAction(Action):
     """
     The ADD action appends elements to a set or mathematically adds to a number attribute.
@@ -65,6 +76,7 @@ def __init__(self, *actions):
         self.remove_actions = []
         self.add_actions = []
         self.delete_actions = []
+        self.list_remove_actions = []
         for action in actions:
             self.add_action(action)
 
@@ -73,6 +85,8 @@ def add_action(self, action):
             self.set_actions.append(action)
         elif isinstance(action, RemoveAction):
             self.remove_actions.append(action)
+        elif isinstance(action, ListRemoveAction):
+            self.list_remove_actions.append(action)
         elif isinstance(action, AddAction):
             self.add_actions.append(action)
         elif isinstance(action, DeleteAction):
@@ -84,6 +98,7 @@ def serialize(self, placeholder_names, expression_attribute_values):
         expression = None
         expression = self._add_clause(expression, 'SET', self.set_actions, placeholder_names, expression_attribute_values)
         expression = self._add_clause(expression, 'REMOVE', self.remove_actions, placeholder_names, expression_attribute_values)
+        expression = self._add_clause(expression, 'REMOVE', self.list_remove_actions, placeholder_names, expression_attribute_values)
         expression = self._add_clause(expression, 'ADD', self.add_actions, placeholder_names, expression_attribute_values)
         expression = self._add_clause(expression, 'DELETE', self.delete_actions, placeholder_names, expression_attribute_values)
         return expression

pynamodb/expressions/update.pyi

@@ -15,6 +15,10 @@ class RemoveAction(Action):
     def __init__(self, path: Path) -> None: ...
 
 
+class ListRemoveAction(Action):
+    def __init__(self, path: Path, *indexes: int) -> None: ...
+
+
 class AddAction(Action):
     def __init__(self, path: Path, subset: Path) -> None: ...
 
@@ -26,6 +30,7 @@ class DeleteAction(Action):
 class Update(object):
     set_actions: List[SetAction]
     remove_actions: List[RemoveAction]
+    list_remove_actions: List[ListRemoveAction]
     add_actions: List[AddAction]
     delete_actions: List[DeleteAction]
     def __init__(self, *actions: Action) -> None: ...

tests/test_expressions.py

@@ -431,6 +431,7 @@ class UpdateExpressionTestCase(TestCase):
 
     def setUp(self):
         self.attribute = UnicodeAttribute(attr_name='foo')
+        self.list_attribute = ListAttribute(attr_name='foo_list', default=[])
 
     def test_set_action(self):
         action = self.attribute.set('bar')
@@ -589,3 +590,26 @@ def test_update(self):
             ':1': {'N': '0'},
             ':2': {'NS': ['0']}
         }
+
+    def test_list_update_remove_by_index(self):
+        update = Update(
+            self.list_attribute.remove_indexes(0),
+        )
+        placeholder_names, expression_attribute_values = {}, {}
+        expression = update.serialize(placeholder_names, expression_attribute_values)
+        assert expression == "REMOVE #0[0]"
+        assert placeholder_names == {'foo_list': '#0'}
+        assert expression_attribute_values == {}
+
+        update = Update(
+            self.list_attribute.remove_indexes(0, 10),
+        )
+        placeholder_names, expression_attribute_values = {}, {}
+        expression = update.serialize(placeholder_names, expression_attribute_values)
+        assert expression == "REMOVE #0[0], #0[10]"
+        assert placeholder_names == {'foo_list': '#0'}
+        assert expression_attribute_values == {}
+
+        with self.assertRaises(ValueError) as e:
+            Update(self.list_attribute.remove_indexes(0, "a"))
+        assert str(e.exception) == "Method 'remove_indexes' arguments must be 'int'"