node: add type signatures

Signed-off-by: Matej Focko <mfocko@redhat.com>

node.py

@@ -1,4 +1,14 @@
+from abc import abstractmethod
 import enum
+from typing import Callable, Optional, Generic, Tuple, TypeVar, Protocol
+
+
+class Comparable(Protocol):
+    """Protocol for annotating comparable types."""
+
+    @abstractmethod
+    def __lt__(self: "Comparable", other: "Comparable") -> bool:
+        pass
 
 
 class NodeType(enum.IntEnum):
@@ -7,17 +17,26 @@ class NodeType(enum.IntEnum):
     BINARY = 2
 
 
-class Node:
+T = TypeVar("T", bound=Comparable)
-    def __init__(self, value, left=None, right=None, parent=None):
+
+
+class Node(Generic[T]):
+    def __init__(
+        self,
+        value: T,
+        left: "Optional[Node[T]]" = None,
+        right: "Optional[Node[T]]" = None,
+        parent: "Optional[Node[T]]" = None,
+    ):
         self.parent = parent
         self.left = left
         self.right = right
 
         self.value = value
-        self.rank = 0
+        self.rank: int = 0
 
     @property
-    def type(self):
+    def type(self) -> NodeType:
         if self.left and self.right:
             return NodeType.BINARY
 
@@ -26,46 +45,58 @@ class Node:
 
         return NodeType.LEAF
 
-    def __repr__(self):
+    def __repr__(self) -> str:
-        return f"Node(value={self.value}, rank={self.rank}, left={self.left}, right={self.right}, parent={self.parent})"
+        return (
+            f"Node(value={self.value}, rank={self.rank}, "
+            f"left={self.left}, right={self.right}, parent={self.parent})"
+        )
 
-    def __str__(self):
+    def __str__(self) -> str:
         return f"Node(value={self.value}, rank={self.rank})"
 
     @staticmethod
-    def height(node):
+    def height(node: "Optional[Node[T]]") -> int:
-        return 1 + max(Node.height(node.left), Node.height(node.right)) if node else -1
+        return (
+            1 + max(Node.height(node.left), Node.height(node.right))
+            if node
+            else -1
+        )
 
     @staticmethod
-    def rank(node):
+    def get_rank(node: "Optional[Node[T]]") -> int:
         return -1 if not node else node.rank
 
     @staticmethod
-    def difference(node, parent=None):
+    def difference(
+        node: "Optional[Node[T]]", parent: "Optional[Node[T]]" = None
+    ) -> int:
         if not parent:
             parent = node.parent if node else None
-        return Node.rank(parent) - Node.rank(node)
+        return Node.get_rank(parent) - Node.get_rank(node)
 
     @staticmethod
-    def differences(node):
+    def differences(node: "Optional[Node[T]]") -> Tuple[int, int]:
-        node_rank = Node.rank(node)
+        node_rank = Node.get_rank(node)
         (left, right) = (node.left, node.right) if node else (None, None)
 
-        return (node_rank - Node.rank(left), node_rank - Node.rank(right))
+        return (
+            node_rank - Node.get_rank(left),
+            node_rank - Node.get_rank(right),
+        )
 
-    def promote(self):
+    def promote(self) -> "Node[T]":
         self.rank += 1
         return self
 
-    def demote(self):
+    def demote(self) -> "Node[T]":
         self.rank -= 1
         return self
 
     @staticmethod
-    def rotate_right(x):
+    def rotate_right(x: "Node[T]") -> "Node[T]":
         parent = x.parent
         y = x.left
-        z = x.right
+        # z = x.right
 
         assert y is not None
         if parent:
@@ -85,9 +116,9 @@ class Node:
         return y
 
     @staticmethod
-    def rotate_left(x):
+    def rotate_left(x: "Node[T]") -> "Node[T]":
         parent = x.parent
-        y = x.left
+        # y = x.left
         z = x.right
 
         assert z is not None
@@ -108,8 +139,10 @@ class Node:
         return z
 
     @staticmethod
-    def find_parent_node(value, node, missing=True):
+    def find_parent_node(
-        new_node = node
+        value: T, node: "Node[T]", missing: bool = True
+    ) -> "Node[T]":
+        new_node: "Optional[Node[T]]" = node
 
         while new_node and (missing or new_node.value != value):
             node = new_node
@@ -118,22 +151,25 @@ class Node:
         return node
 
     @staticmethod
-    def search(value, node):
+    def search(value: T, node: "Optional[Node[T]]") -> "Optional[Node[T]]":
         while node and node.value != value:
             node = node.left if value < node.value else node.right
 
         return node
 
     @staticmethod
-    def minimum(node):
+    def minimum(node: "Node[T]") -> "Node[T]":
         while node.left:
             node = node.left
 
         return node
 
     @staticmethod
-    def maximum(node):
+    def maximum(node: "Node[T]") -> "Node[T]":
         while node.right:
             node = node.right
 
         return node
+
+
+RotateFunction = Callable[[Node[T]], Node[T]]