Created
January 7, 2021 18:49
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Snippet of how the State design pattern works
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from stately.base import State | |
from stately.enums import PersonStateKey | |
_INITIAL_STAMINA = 5 | |
_WALKING_EFFORT = 2 | |
_RUNNING_EFFORT = 3 | |
_RESTING_POWER = 5 | |
# Placed Person here to avoid cyclic dependencies. The con though is that too | |
# much code may end up living in one module. An alternative solution is to | |
# actually defer the PassiveState import until the constructor of Person is | |
# invoked. See the following resource for more tips: | |
# https://stackabuse.com/python-circular-imports/ | |
class Person(State): | |
def __init__(self, name: str): | |
self.name = name | |
self.stamina = _INITIAL_STAMINA | |
self.state = PassiveState(self) | |
def get_state_key(self) -> PersonStateKey: | |
return self.state.get_state_key() | |
def is_tired(self) -> bool: | |
return self.stamina < 0 | |
def can_move(self, effort: int) -> bool: | |
return self.stamina >= effort | |
def lose_energy(self, effort: int): | |
self.stamina -= effort | |
def gain_energy(self, effort: int): | |
self.stamina += effort | |
def change_state(self, state: State): | |
self.state = state | |
def walking(self): | |
self.state.walking() | |
def running(self): | |
self.state.running() | |
def resting(self): | |
self.state.resting() | |
class ActiveState(State): | |
def __init__(self, context: Person): | |
self.person: Person = context | |
def get_state_key(self): | |
return PersonStateKey.ACTIVE | |
def walking(self): | |
print(f"{self.person.name} is walking") | |
self.person.lose_energy(_WALKING_EFFORT) | |
if self.person.is_tired(): | |
print(f"{self.person.name} needs a break from walking") | |
self.person.change_state(PassiveState(self.person)) | |
def running(self): | |
print(f"{self.person.name} is running") | |
self.person.lose_energy(_RUNNING_EFFORT) | |
if self.person.is_tired(): | |
print(f"{self.person.name} needs a break from running") | |
self.person.change_state(PassiveState(self.person)) | |
def resting(self): | |
print(f"{self.person.name} is going home to get some rest") | |
self.person.gain_energy(_RESTING_POWER) | |
self.person.change_state(PassiveState(self.person)) | |
class PassiveState(State): | |
def __init__(self, context: Person): | |
self.person: Person = context | |
def get_state_key(self): | |
return PersonStateKey.PASSIVE | |
def walking(self): | |
if self.person.can_move(_WALKING_EFFORT): | |
print(f"{self.person.name} is walking after a break") | |
self.person.lose_energy(_WALKING_EFFORT) | |
self.person.change_state(ActiveState(self.person)) | |
else: | |
print(f"{self.person.name} cannot walk and needs a break") | |
def running(self): | |
if self.person.can_move(_RUNNING_EFFORT): | |
print(f"{self.person.name} is running after break") | |
self.person.lose_energy(_RUNNING_EFFORT) | |
self.person.change_state(ActiveState(self.person)) | |
else: | |
print(f"{self.person.name} cannot run and needs a break") | |
def resting(self): | |
print(f"{self.person.name} is resting peacefully") | |
self.person.gain_energy(_RESTING_POWER) |
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