diff --git a/pocketflow/__init__.py b/pocketflow/__init__.py
index a7203df..5534c23 100644
--- a/pocketflow/__init__.py
+++ b/pocketflow/__init__.py
@@ -1,32 +1,33 @@
 import asyncio, warnings, copy, time
+from typing import Dict, Any, Optional, List, Union
 
 class BaseNode:
-    def __init__(self): self.params,self.successors={},{}
-    def set_params(self,params): self.params=params
-    def next(self,node,action="default"):
+    def __init__(self) -> None: self.params,self.successors={},{}
+    def set_params(self,params: Dict[str, Any]) -> None: self.params=params
+    def next(self,node: 'BaseNode',action: str="default") -> 'BaseNode':
         if action in self.successors: warnings.warn(f"Overwriting successor for action '{action}'")
         self.successors[action]=node; return node
-    def prep(self,shared): pass
-    def exec(self,prep_res): pass
-    def post(self,shared,prep_res,exec_res): pass
-    def _exec(self,prep_res): return self.exec(prep_res)
-    def _run(self,shared): p=self.prep(shared); e=self._exec(p); return self.post(shared,p,e)
-    def run(self,shared): 
+    def prep(self,shared: Dict[str, Any]) -> Any: pass
+    def exec(self,prep_res: Any) -> Any: pass
+    def post(self,shared: Dict[str, Any],prep_res: Any,exec_res: Any) -> Any: pass
+    def _exec(self,prep_res: Any) -> Any: return self.exec(prep_res)
+    def _run(self,shared: Dict[str, Any]) -> Any: p=self.prep(shared); e=self._exec(p); return self.post(shared,p,e)
+    def run(self,shared: Dict[str, Any]) -> Any: 
         if self.successors: warnings.warn("Node won't run successors. Use Flow.")  
         return self._run(shared)
-    def __rshift__(self,other): return self.next(other)
-    def __sub__(self,action):
+    def __rshift__(self,other: 'BaseNode') -> 'BaseNode': return self.next(other)
+    def __sub__(self,action: str) -> '_ConditionalTransition':
         if isinstance(action,str): return _ConditionalTransition(self,action)
         raise TypeError("Action must be a string")
 
 class _ConditionalTransition:
-    def __init__(self,src,action): self.src,self.action=src,action
-    def __rshift__(self,tgt): return self.src.next(tgt,self.action)
+    def __init__(self,src: BaseNode,action: str) -> None: self.src,self.action=src,action
+    def __rshift__(self,tgt: BaseNode) -> BaseNode: return self.src.next(tgt,self.action)
 
 class Node(BaseNode):
-    def __init__(self,max_retries=1,wait=0): super().__init__(); self.max_retries,self.wait=max_retries,wait
-    def exec_fallback(self,prep_res,exc): raise exc
-    def _exec(self,prep_res):
+    def __init__(self,max_retries: int=1,wait: Union[int, float]=0) -> None: super().__init__(); self.max_retries,self.wait=max_retries,wait
+    def exec_fallback(self,prep_res: Any,exc: Exception) -> Any: raise exc
+    def _exec(self,prep_res: Any) -> Any:
         for self.cur_retry in range(self.max_retries):
             try: return self.exec(prep_res)
             except Exception as e:
@@ -34,67 +35,67 @@ class Node(BaseNode):
                 if self.wait>0: time.sleep(self.wait)
 
 class BatchNode(Node):
-    def _exec(self,items): return [super(BatchNode,self)._exec(i) for i in (items or [])]
+    def _exec(self,items: Optional[List[Any]]) -> List[Any]: return [super(BatchNode,self)._exec(i) for i in (items or [])]
 
 class Flow(BaseNode):
-    def __init__(self,start=None): super().__init__(); self.start_node=start
-    def start(self,start): self.start_node=start; return start
-    def get_next_node(self,curr,action):
+    def __init__(self,start: Optional[BaseNode]=None) -> None: super().__init__(); self.start_node=start
+    def start(self,start: BaseNode) -> BaseNode: self.start_node=start; return start
+    def get_next_node(self,curr: BaseNode,action: Optional[str]) -> Optional[BaseNode]:
         nxt=curr.successors.get(action or "default")
         if not nxt and curr.successors: warnings.warn(f"Flow ends: '{action}' not found in {list(curr.successors)}")
         return nxt
-    def _orch(self,shared,params=None):
+    def _orch(self,shared: Dict[str, Any],params: Optional[Dict[str, Any]]=None) -> Any:
         curr,p,last_action =copy.copy(self.start_node),(params or {**self.params}),None
         while curr: curr.set_params(p); last_action=curr._run(shared); curr=copy.copy(self.get_next_node(curr,last_action))
         return last_action
-    def _run(self,shared): p=self.prep(shared); o=self._orch(shared); return self.post(shared,p,o)
-    def post(self,shared,prep_res,exec_res): return exec_res
+    def _run(self,shared: Dict[str, Any]) -> Any: p=self.prep(shared); o=self._orch(shared); return self.post(shared,p,o)
+    def post(self,shared: Dict[str, Any],prep_res: Any,exec_res: Any) -> Any: return exec_res
 
 class BatchFlow(Flow):
-    def _run(self,shared):
+    def _run(self,shared: Dict[str, Any]) -> Any:
         pr=self.prep(shared) or []
         for bp in pr: self._orch(shared,{**self.params,**bp})
         return self.post(shared,pr,None)
 
 class AsyncNode(Node):
-    async def prep_async(self,shared): pass
-    async def exec_async(self,prep_res): pass
-    async def exec_fallback_async(self,prep_res,exc): raise exc
-    async def post_async(self,shared,prep_res,exec_res): pass
-    async def _exec(self,prep_res): 
+    async def prep_async(self,shared: Dict[str, Any]) -> Any: pass
+    async def exec_async(self,prep_res: Any) -> Any: pass
+    async def exec_fallback_async(self,prep_res: Any,exc: Exception) -> Any: raise exc
+    async def post_async(self,shared: Dict[str, Any],prep_res: Any,exec_res: Any) -> Any: pass
+    async def _exec(self,prep_res: Any) -> Any: 
         for i in range(self.max_retries):
             try: return await self.exec_async(prep_res)
             except Exception as e:
                 if i==self.max_retries-1: return await self.exec_fallback_async(prep_res,e)
                 if self.wait>0: await asyncio.sleep(self.wait)
-    async def run_async(self,shared): 
+    async def run_async(self,shared: Dict[str, Any]) -> Any: 
         if self.successors: warnings.warn("Node won't run successors. Use AsyncFlow.")  
         return await self._run_async(shared)
-    async def _run_async(self,shared): p=await self.prep_async(shared); e=await self._exec(p); return await self.post_async(shared,p,e)
-    def _run(self,shared): raise RuntimeError("Use run_async.")
+    async def _run_async(self,shared: Dict[str, Any]) -> Any: p=await self.prep_async(shared); e=await self._exec(p); return await self.post_async(shared,p,e)
+    def _run(self,shared: Dict[str, Any]) -> Any: raise RuntimeError("Use run_async.")
 
 class AsyncBatchNode(AsyncNode,BatchNode):
-    async def _exec(self,items): return [await super(AsyncBatchNode,self)._exec(i) for i in items]
+    async def _exec(self,items: Optional[List[Any]]) -> List[Any]: return [await super(AsyncBatchNode,self)._exec(i) for i in items]
 
 class AsyncParallelBatchNode(AsyncNode,BatchNode):
-    async def _exec(self,items): return await asyncio.gather(*(super(AsyncParallelBatchNode,self)._exec(i) for i in items))
+    async def _exec(self,items: Optional[List[Any]]) -> List[Any]: return await asyncio.gather(*(super(AsyncParallelBatchNode,self)._exec(i) for i in items))
 
 class AsyncFlow(Flow,AsyncNode):
-    async def _orch_async(self,shared,params=None):
+    async def _orch_async(self,shared: Dict[str, Any],params: Optional[Dict[str, Any]]=None) -> Any:
         curr,p,last_action =copy.copy(self.start_node),(params or {**self.params}),None
         while curr: curr.set_params(p); last_action=await curr._run_async(shared) if isinstance(curr,AsyncNode) else curr._run(shared); curr=copy.copy(self.get_next_node(curr,last_action))
         return last_action
-    async def _run_async(self,shared): p=await self.prep_async(shared); o=await self._orch_async(shared); return await self.post_async(shared,p,o)
-    async def post_async(self,shared,prep_res,exec_res): return exec_res
+    async def _run_async(self,shared: Dict[str, Any]) -> Any: p=await self.prep_async(shared); o=await self._orch_async(shared); return await self.post_async(shared,p,o)
+    async def post_async(self,shared: Dict[str, Any],prep_res: Any,exec_res: Any) -> Any: return exec_res
 
 class AsyncBatchFlow(AsyncFlow,BatchFlow):
-    async def _run_async(self,shared):
+    async def _run_async(self,shared: Dict[str, Any]) -> Any:
         pr=await self.prep_async(shared) or []
         for bp in pr: await self._orch_async(shared,{**self.params,**bp})
         return await self.post_async(shared,pr,None)
 
 class AsyncParallelBatchFlow(AsyncFlow,BatchFlow):
-    async def _run_async(self,shared): 
+    async def _run_async(self,shared: Dict[str, Any]) -> Any: 
         pr=await self.prep_async(shared) or []
         await asyncio.gather(*(self._orch_async(shared,{**self.params,**bp}) for bp in pr))
         return await self.post_async(shared,pr,None)
\ No newline at end of file