Python-状态机模式的实现

为什么要需要Python状态机

原因：解决代码冗余处理效率低的问题
原有模式代码

class Connection: 
""" 普通方案，好多个判断语句，效率低下"""
	def __init__(self): 
		self.state = 'CLOSED'
	def read(self): 
		if self.state != 'OPEN': 
			raise RuntimeError('Not open')
		print('reading')
	def write(self, data): 
		if self.state != 'OPEN': 
			raise RuntimeError('Not open') 
		print('writing')
	def open(self): 
		if self.state == 'OPEN': 
			raise RuntimeError('Already open') 
		self.state = 'OPEN'
	def close(self): 
		if self.state == 'CLOSED': 
			raise RuntimeError('Already closed') 
		self.state = 'CLOSED'
		

状态机模式的实现

原理：为每一个状态定义一个对象，并通过实例方法在不同的状态之间进行转换

class Connection1:
 """ 新方案——对每个状态定义一个类，Connection1类为主类"""
	def __init__(self): 
	#初始状态为closed状态，为ClosedConnectionState的实例
		self.new_state(ClosedConnectionState)
	def new_state(self, newstate): 
		self._state = newstate # Delegate to the state class
	def read(self): 
	#调用的是所属实例的方法（Close/Open）
		return self._state.read(self)
	def write(self, data): 
		return self._state.write(self, data)
	def open(self): 
		return self._state.open(self)
	def close(self): 
		return self._state.close(self)


# Connection state base class 
class ConnectionState: 
	@staticmethod 
	def read(conn): 
	#子类必须实现父类的方法，否则报下列错误
		raise NotImplementedError()
	@staticmethod 
	def write(conn, data): 
		raise NotImplementedError()
	@staticmethod 
	def open(conn): 
		raise NotImplementedError()
	@staticmethod 
	def close(conn): 
		raise NotImplementedError()
		

# Implementation of different states 
class ClosedConnectionState(ConnectionState): 
	@staticmethod 
	def read(conn): 
		raise RuntimeError('Not open')
	@staticmethod 
	def write(conn, data): 
		raise RuntimeError('Not open')
	@staticmethod 
	def open(conn): 
		conn.new_state(OpenConnectionState)
	@staticmethod 
	def close(conn): 
		raise RuntimeError('Already closed')
	
	
class OpenConnectionState(ConnectionState): 
	@staticmethod 
	def read(conn): 
		print('reading')
	@staticmethod 
	def write(conn, data): 
		print('writing')
	@staticmethod 
	def open(conn): 
		raise RuntimeError('Already open')
	@staticmethod 
	def close(conn): 
	#转换为Close实例，调用父类的new_state方法
		conn.new_state(ClosedConnectionState)
		

代码调用

c = Connection1()
c._state