diff --git a/src/cpl_query/extension/iterable_abc.py b/src/cpl_query/extension/iterable_abc.py
index 45135c6e..e45d7815 100644
--- a/src/cpl_query/extension/iterable_abc.py
+++ b/src/cpl_query/extension/iterable_abc.py
@@ -158,7 +158,7 @@ class IterableABC(ABC, list):
         """
         pass
 
-    def extend(self, __iterable: Iterable) -> None:
+    def extend(self, __iterable: Iterable) -> 'IterableABC':
         r"""Adds elements of given list to list
 
         Parameter
@@ -169,6 +169,8 @@ class IterableABC(ABC, list):
         for value in __iterable:
             self.append(value)
 
+        return self
+
     @abstractmethod
     def last(self) -> any:
         r"""Returns last element
@@ -290,6 +292,24 @@ class IterableABC(ABC, list):
         """
         pass
 
+    def select(self, _f: Callable) -> 'IterableABC':
+        r"""Formats each element of list to a given format
+
+        Returns
+        -------
+            :class: `cpl_query.extension.iterable_abc.IterableABC`
+        """
+        pass
+
+    def select_many(self, _f: Callable) -> 'IterableABC':
+        r"""Flattens resulting lists to one
+
+        Returns
+        -------
+            :class: `cpl_query.extension.iterable_abc.IterableABC`
+        """
+        pass
+
     @abstractmethod
     def single(self) -> any:
         r"""Returns one single element of list
diff --git a/unittests/unittests_query/query_test_case.py b/unittests/unittests_query/query_test_case.py
index 00d4fed8..74fff280 100644
--- a/unittests/unittests_query/query_test_case.py
+++ b/unittests/unittests_query/query_test_case.py
@@ -161,9 +161,9 @@ class QueryTestCase(unittest.TestCase):
     def test_for_each(self):
         users = []
         self._tests.for_each(lambda user: (
-                users.append(user)
-            )
+            users.append(user)
         )
+                             )
 
         self.assertEqual(len(users), len(self._tests))
 
@@ -239,6 +239,35 @@ class QueryTestCase(unittest.TestCase):
 
         self.assertEqual(l_res, res)
 
+    def test_select(self):
+        range_list = List(int, range(0, 100))
+        selected_range = range_list.select(lambda x: x + 1)
+
+        modulo_range = []
+        for x in range(0, 100):
+            if x % 2 == 0:
+                modulo_range.append(x)
+        self.assertEqual(selected_range.to_list(), list(range(1, 101)))
+        self.assertEqual(range_list.where(lambda x: x % 2 == 0).to_list(), modulo_range)
+
+    def test_select_many(self):
+        range_list = List(int, range(0, 100))
+        selected_range = range_list.select(lambda x: [x, x])
+
+        self.assertEqual(selected_range, [[x, x] for x in range(0, 100)])
+        self.assertEqual(selected_range.select_many(lambda x: x).to_list(), [_x for _l in [2 * [x] for x in range(0, 100)] for _x in _l])
+
+        class TestClass:
+            def __init__(self, i, is_sub=False):
+                self.i = i
+                if is_sub:
+                    return
+                self.elements = [TestClass(x, True) for x in range(0, 10)]
+
+        elements = List(TestClass, [TestClass(i) for i in range(0, 100)])
+        selected_elements = elements.select_many(lambda x: x.elements).select(lambda x: x.i)
+        self.assertEqual(selected_elements.where(lambda x: x == 0).count(), 100)
+
     def test_single(self):
         res = self._tests.where(lambda u: u.address.nr == self._t_user.address.nr)
         s_res = self._tests.where(lambda u: u.address.nr == self._t_user.address.nr).single()