8.13. State Machine¶
8.13.1. Rationale¶
EN: State Machine
PL: Maszyna Stanów
Type: class
8.13.2. Use Cases¶
StateMachine imposes a structure to automatically change the implementation from one object to the next
The current implementation represents the state that a system is in
System behaves differently from one state to the next
The code that moves the system from one state to the next
Each state can be
run()to perform its behaviorYou can pass it an
inputobject so it can tell you what new state to move to based on thatinputEach State object decides what other states it can move to, based on the
inputEach State object has its own little State table
There is a single master state transition table for the whole system
8.13.3. Design¶
statemachine TrafficLight:
Red -> Amber
Amber (if previous == Red) -> Green
Green -> Amber
Amber (if previous == Green) -> Red
Red.wait = sleep(2)
Amber.wait = sleep(1)
Green.wait = sleep(2)
8.13.4. Implementation¶
from abc import ABCMeta, abstractmethod
class Tool(metaclass=ABCMeta):
@abstractmethod
def mouse_down(self) -> None:
pass
@abstractmethod
def mouse_up(self) -> None:
pass
class SelectionTool(Tool):
def mouse_down(self) -> None:
print('Selection icon')
def mouse_up(self) -> None:
print('Draw dashed rectangle')
class BrushTool(Tool):
def mouse_down(self) -> None:
print('Brush icon')
def mouse_up(self) -> None:
print('Draw line')
class Canvas:
__current_tool: Tool
def mouse_down(self) -> None:
self.__current_tool.mouse_down()
def mouse_up(self) -> None:
self.__current_tool.mouse_up()
def get_current_tool(self):
return self.__current_tool
def set_current_tool(self, newtool: Tool):
self.__current_tool = newtool
if __name__ == '__main__':
canvas = Canvas()
canvas.set_current_tool(SelectionTool())
canvas.mouse_down()
# Selection icon
canvas.mouse_up()
# Draw dashed rectangle