当 Python 只应附加到一个列表时，它会附加到两个列表

Posted 2023-02-23

【中文标题】当 Python 只应附加到一个列表时，它会附加到两个列表

【英文标题】：Python appending to two lists when it should only append to one

【发布时间】：2011-10-14 17:56:54

【问题描述】：

我有一个名为 teams 的列表，其中包含两个对象，它们是同一类的对象，它们都有一个“成员”列表。我将分别附加到这些列表中。请参阅 Fight.AddParticipant 但我附加的两个参与者对象似乎最终出现在两个团队对象中，这是意外行为。为什么会这样？

代码：

class Fight:
    participants = []
    teams = []
    attacked = []
    fighting = 0

    def MakeTeams(self, team):
        self.teams.append(team)

    def NumParticipants(self, teamnum = None):
        if (teamnum != None):
            return len(self.teams[teamnum].members)
        else:
            return len(self.participants)


    def AddParticipant(self, participant, team):
        self.participants.append(participant)
        ref = self.participants[-1]
        self.teams[team].members.append(ref)
        # print self.teams[1].members[0].name

    def SetFighting(self):
        self.fighting = self.NumParticipants()

    def AnnounceFight(self):
        print 'A battle between', self.NumParticipants(), 'fighters has begun!\n\n'
        self.AnnounceTeams()

    def AnnounceTeams(self):
        print ''
        for team in self.teams:
            print "Team name:", team.name
            print "Team morale:", team.morale
            for member in team.members:
                print member.name


class Participant:
    name = ""
    race = ""
    sex = ""
    hp = 0
    strength = 0
    agility = 0
    weapon = ""
    alive = True

    def __init__(self, name, race, sex, hp, strength, agility, weapon, alive = True):
        self.name = name
        self.race = race
        self.sex = sex
        self.hp = hp
        self.strength = strength
        self.agility = agility
        self.weapon = weapon
        self.alive = alive


class Team:
    name = ""
    members = []
    morale = 0

    def __init__(self, name, morale):
        self.name = name
        self.morale = morale

Fight = Fight()
Fight.MakeTeams(Team('Smart', 1))
Fight.MakeTeams(Team('Dumb', 1))
Fight.AddParticipant(Participant("Foo", "Human", "Female", 15, 15, 20, "Knife"), 0)
Fight.AddParticipant(Participant("Bar", "Human", "Male", 15, 15, 20, "Sabre"), 1)
Fight.SetFighting()
Fight.AnnounceFight()

【问题讨论】：

原因可能是您的成员变量是类属性而不是实例属性。因此，在 Team 类的所有实例中都可以看到成员的变化。

【参考方案1】：

在所有类中，您都希望像这样初始化实例变量：

def __init__(self):
    self.participants = []
    self.teams = []
    self.attacked = []
    self.fighting = 0

这样，它们对于每个战斗、参与者、团队都是独立的，而不是为所有战斗、参与者或团队共享。

【参考方案2】：

您已将列表设为类属性，这意味着列表由所有实例共享。这是同一个列表。您应该制作列表实例属性。通过在类的__init__（构造函数）方法中创建它们来做到这一点。

【参考方案3】：

我认为您的意思是成员成为实例的成员，而是使它们成为类成员。试试这个：

class Team:
    name = ""
    morale = 0

    def __init__(self, name, morale):
        self.members = []
        self.name = name
        self.morale = morale

您可能希望将所有其他变量移动到构造函数中，而不是将它们保留为类变量。类变量由所有实例共享并归类所有。