[英]Call Python Method on Class Attribute Change
我正在编写一个API解析Twitter机器人,对OOP来说是个新手。 我有一些依赖于全局变量的现有Python代码,并认为我可以借此机会学习。
我有以下Team类,这些类在解析API时会更新,并且希望能够在类属性更改时调用完全不相关的(外部)方法。
class Team(object):
def __init__(self, team_name, tri_code, goals, shots, goalie_pulled):
self.team_name = team_name
self.tri_code = tri_code
self.goals = goals
self.shots = shots
self.goalie_pulled = goalie_pulled
当goalie_pulled
是改变现有实例Team
,我想下面的方法被调用(伪代码):
def goalie_pulled_tweet(team):
tweet = "{} has pulled their goalie with {} remaining!".format(team.team_name, game.period_remain)
send_tweet(tweet)
两件事情 -
goalie_pulled
属性已更改,如何在Team
类中调用goalie_pulled_tweet
? Game
对象的实例,还是也需要将其传递给该变量? 您应该看看属性类。 基本上,它使您可以封装行为和私有成员,而消费者甚至不会注意到它。
在您的示例中,您可能具有goalie_pulled
属性:
class Team(object):
def __init__(self, team_name, tri_code, goals, shots, goalie_pulled):
# Notice the identation here. This is very important.
self.team_name = team_name
self.tri_code = tri_code
self.goals = goals
self.shots = shots
# Prefix your field with an underscore, this is Python standard way for defining private members
self._goalie_pulled = goalie_pulled
@property
def goalie_pulled(self):
return self._goalie_pulled
@goalie_pulled.setter
def goalie_pulled(self, new_value):
self._goalie_pulled = new_value
goalie_pulled_tweet(self) #self is the current Team instance
从消费者的角度来看:
team = create_team_instance()
# goalie_pulled_tweet is called
team.goalie_pulled = 'some_value'
我建议您尽可能(并且必须)使用属性,因为它们是一种很好的抽象方法。
从设计的角度来看,使用pull_goalie
方法会更有意义。
类是创建更有意义的抽象的工具。 拉守门员是一个动作。 如果您认为Team
代表了现实生活中的团队,那么说“团队拔了守门员!”更有意义。 而不是“团队将他们的拉高目标属性设置为X玩家!”
class Team(object):
...
def pull_goalie(self, player):
self.pulled_goalie = player
tweet = '<your format string>'.format(
self.pulled_goalie,
# Yes, your Team *could* store a reference to the current game.
# It's hard to tell if that makes sense in your program without more context.
self.game.period_remaining
)
我打算推荐一个属性,但是我认为这可以解决当前的问题,而无需考虑更广泛的设计清晰度。
注意:Python中没有“私有”属性。 有一个约定,以单个下划线( self._pulled_goalie
)开头的属性被视为私有,但这只是为了使使用您的代码的人知道,他们不能一直依赖于该值来始终执行他们认为会做的事情。 (即,它不是代码公共合同的一部分,您可以更改它而不会发出警告。)
编辑:要在Game
对象上创建一个register_team
方法,您可以做这样的事情:
class Game(object):
def __init__(<stuff>):
...
self.teams = {}
...
def register_team(self, team):
if len(self.teams) > 1:
raise ValueError(
"Too many teams! Cannot register {} for {}"
.format(team, game)
)
self.teams[team] = team
team.game = self
def unregister_team(self, team):
try:
del self.teams[team]
except KeyError:
pass
team.game = None
请注意,通过使用字典,可以多次调用register_team
和unregiser_team
而不会产生不良影响。
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