Move ChilrenList out of Tree class

It can be cumbersome to deal with this class if we want
to instantiate if from the outside.

Author: boriel

src/ast/tree.py

@@ -6,6 +6,7 @@
 from typing import Iterable
 from typing import List
 from typing import Optional
+from typing import Union
 
 from src.api.errors import Error
 
@@ -29,77 +30,20 @@ class Tree:
     """
     parent: Optional['Tree'] = None
 
-    class ChildrenList:
-        def __init__(self, node: 'Tree'):
-            assert isinstance(node, Tree)
-            self.parent = node  # Node having this children
-            self._children: List['Tree'] = []
-
-        def __getitem__(self, key):
-            if isinstance(key, int):
-                return self._children[key]
-
-            result = Tree.ChildrenList(self.parent)
-            for x in self._children[key]:
-                result.append(x)
-            return result
-
-        def __setitem__(self, key, value):
-            assert value is None or isinstance(value, Tree)
-            if value is not None:
-                value.parent = self.parent
-            self._children[key] = value
-
-        def __delitem__(self, key):
-            self._children[key].parent = None
-            del self._children[key]
-
-        def append(self, value):
-            assert isinstance(value, Tree)
-            value.parent = self.parent
-            self._children.append(value)
-
-        def insert(self, pos, value):
-            assert isinstance(value, Tree)
-            value.parent = self.parent
-            self._children.insert(pos, value)
-
-        def pop(self, pos=-1):
-            result = self._children.pop(pos)
-            result.parent = None
-            return result
-
-        def __len__(self):
-            return len(self._children)
-
-        def __add__(self, other):
-            if not isinstance(other, Tree.ChildrenList):
-                assert isinstance(other, collections.Container)
-
-            result = Tree.ChildrenList(self.parent)
-            for x in self:
-                result.append(x)
-            for x in other:
-                result.append(x)
-            return result
-
-        def __repr__(self):
-            return "%s:%s" % (self.parent.__repr__(), str([x.__repr__() for x in self._children]))
-
     def __init__(self):
-        self._children = Tree.ChildrenList(self)
+        self._children = ChildrenList(self)
 
     @property
     def children(self):
         return self._children
 
     @children.setter
     def children(self, value: Iterable):
-        assert isinstance(value, collections.abc.Iterable)
+        assert isinstance(value, collections.Iterable)
         while len(self.children):
             self.children.pop()
 
-        self._children = Tree.ChildrenList(self)
+        self._children = ChildrenList(self)
         for x in value:
             self.children.append(x)
 
@@ -136,3 +80,63 @@ def prependChild(self, node: 'Tree'):
         """ Inserts the given node at the beginning of the children list
         """
         self.children.insert(0, node)
+
+
+class ChildrenList:
+    parent: Tree
+
+    def __init__(self, node: Tree):
+        assert isinstance(node, Tree)
+        self.parent = node  # Node having this children
+        self._children: List[Tree] = []
+
+    def __getitem__(self, key: Union[int, slice]):
+        if isinstance(key, int):
+            return self._children[key]
+
+        result = ChildrenList(self.parent)
+        for x in self._children[key]:
+            result.append(x)
+        return result
+
+    def __setitem__(self, key, value: Optional[Tree]):
+        assert value is None or isinstance(value, Tree)
+        if value is not None:
+            value.parent = self.parent
+        self._children[key] = value
+
+    def __delitem__(self, key):
+        self._children[key].parent = None
+        del self._children[key]
+
+    def append(self, value: Tree):
+        assert isinstance(value, Tree)
+        value.parent = self.parent
+        self._children.append(value)
+
+    def insert(self, pos: int, value: Tree):
+        assert isinstance(value, Tree)
+        value.parent = self.parent
+        self._children.insert(pos, value)
+
+    def pop(self, pos: int = -1):
+        result = self._children.pop(pos)
+        result.parent = None
+        return result
+
+    def __len__(self):
+        return len(self._children)
+
+    def __add__(self, other):
+        if not isinstance(other, ChildrenList):
+            assert isinstance(other, collections.Container)
+
+        result = ChildrenList(self.parent)
+        for x in self:
+            result.append(x)
+        for x in other:
+            result.append(x)
+        return result
+
+    def __repr__(self):
+        return f"{self.parent.__repr__()}:{str([x.__repr__() for x in self._children])}"