如何按日期对对象和属性进行排序？答案

【问题标题】：How to sort objects and attributes by date?如何按日期对对象和属性进行排序？
【发布时间】：2023-03-22 12:14:01
【问题描述】：

我有下一个代码：

class Petshop():
    def __init__(self, entryDate, name, ownerName):
        self.entryDate = entryDate
        self.name = name
        self.ownerName = ownerName

class Pets():
    def __init__(self):
        self.petsList = []
    
    def addPets(self, entryDate, name, ownerName):
        entry_pet = Petshop(entryDate, name, ownerName)
        self.petsList.append(entry_pet)
    
    def printPets(self):
        for pet in self.petsList:
            if pet.entryDate == pet.entryDate:#Here I try to sort by date
                print("---------------",pet.entryDate,'------------------')
                print("Name:", pet.name)
                print("Owner name:", pet.ownerName)

pet = Pets()

pet.addPets('04/13/2021','Pinky', 'David Smith')
pet.addPets('07/10/2020', 'Charlie', 'Joe Davis')
pet.addPets('12/22/2018', 'Teddy', 'Carl Johnson')
pet.addPets('07/10/2020', 'Kenny', 'Susan Jones')
pet.addPets('04/13/2021','Max', 'Bryan Miller')
pet.addPets('07/10/2020', 'Buddy', 'Kathy Brown')
pet.printPets()

使用该代码我想按日期对宠物条目进行排序，因此例如我希望打印下一个：

--------------- 04/13/2021 ------------------
Name: Pinky
Owner name: David Smith
Name: Max
Owner name: Bryan Miller
--------------- 07/10/2020 ------------------
Name: Charlie
Owner name: Joe Davis
Name: Kenny
Owner name: Susan Jones
Name: Buddy
Owner name: Kathy Brown
--------------- 12/22/2018 ------------------
Name: Teddy
Owner name: Carl Johnson

但我不是这样打印每个对象，这不是我所期望的：

--------------- 04/13/2021 ------------------
Name: Pinky
Owner name: David Smith
--------------- 07/10/2020 ------------------
Name: Charlie
Owner name: Joe Davis
--------------- 12/22/2018 ------------------
Name: Teddy
Owner name: Carl Johnson
--------------- 07/10/2020 ------------------
Name: Kenny
Owner name: Susan Jones
--------------- 04/13/2021 ------------------
Name: Max
Owner name: Bryan Miller
--------------- 07/10/2020 ------------------
Name: Buddy
Owner name: Kathy Brown

我尝试在printPets() 中进行某种排序，但它不起作用。所以我来这里寻求帮助。谢谢！

【问题讨论】：

你为什么期望在所有宠物的循环中比较一个宠物的 entryDate 与它自己，以对任何东西进行排序？你也没有做任何分组，你得到的输出不应该是意外的。
如果您使用datetime 对象来存储您的日期，您可以使用datetime 对象的排序属性，而无需使用字符串。

标签： python list sorting dictionary oop

【解决方案1】：

您可以在创建 petsList 时导入 datetime 并比较日期：

from datetime import datetime

def getDateFromStr(date):
    date_list = []
    for i in date.split('/'):
        date_list.append(int(i))
    # date_list = list(map(lambda x: int(x), date.split('/')))
    return datetime(date_list[2], date_list[0], date_list[1]).date()

class Petshop():
    def __init__(self, entryDate, name, ownerName):
        self.entryDate = entryDate
        self.name = name
        self.ownerName = ownerName

class Pets():
    def __init__(self):
        self.petsList = []
    
    def addPets(self, entryDate, name, ownerName):
        entry_pet = Petshop(entryDate, name, ownerName)
        # creating petsList sorted by date already
        if len(self.petsList) == 0:
            self.petsList.append(entry_pet)
        else:
            for i, pet in enumerate(self.petsList):
                if getDateFromStr(pet.entryDate) < getDateFromStr(entryDate):
                    self.petsList.insert(i, entry_pet)
                    break
                elif i == len(self.petsList) - 1:
                    self.petsList.append(entry_pet)
                    break
    
    def printPets(self):
        for pet in self.petsList:
            if pet.entryDate == pet.entryDate:#Here I try to sort by date
                print("---------------",pet.entryDate,'------------------')
                print("Name:", pet.name)
                print("Owner name:", pet.ownerName)

pet = Pets()

pet.addPets('04/13/2021','Pinky', 'David Smith')
pet.addPets('07/10/2020', 'Charlie', 'Joe Davis')
pet.addPets('12/22/2018', 'Teddy', 'Carl Johnson')
pet.addPets('07/10/2020', 'Kenny', 'Susan Jones')
pet.addPets('04/13/2021','Max', 'Bryan Miller')
pet.addPets('07/10/2020', 'Buddy', 'Kathy Brown')
pet.printPets()

【讨论】：

【解决方案2】：

itertools.groupby 就是你要找的东西：

    def printPets(self):
        self.petsList.sort(key=lambda p: p.entryDate)
        for group in groupby(self.petsList, key=lambda p: p.entryDate):
            ls = list(group)
            print("---------------", ls[0], '------------------')
            for pet in list(ls[1]):
                print("Name:", pet.name)
                print("Owner name:", pet.ownerName)

【讨论】：

【解决方案3】：

您可以将sorted() 与作为key 的参数传递的lambda 函数一起使用。编辑：这段代码应该完全符合您的期望。即每个不同的日期打印一个输入日期。

    def printPets(self):
      for inputdate in sorted(list(set(i.entryDate for i in self.petsList))):
          print("---------------",inputdate,'------------------')
          for pet in list(filter(lambda x: x.entryDate == inputdate, self.petsList)):
            print("Name:", pet.name)
            print("Owner name:", pet.ownerName)

【讨论】：

【解决方案4】：

您必须将魔术方法 __lt__ 添加到您的类中才能进行排序。

class Petshop():
    def __init__(self, entryDate, name, ownerName):
        self.entryDate = entryDate
        self.name = name
        self.ownerName = ownerName

    def __lt__(self, other):
        return self.entryDate < other.entryDate


class Pets():
    def __init__(self):
        self.petsList = []

    def addPets(self, entryDate, name, ownerName):
        entry_pet = Petshop(entryDate, name, ownerName)
        self.petsList.append(entry_pet)

    def printPets(self):
        for pet in sorted(self.petsList):
            if pet.entryDate == pet.entryDate:  # Here I try to sort by date
                print("---------------", pet.entryDate, '------------------')
                print("Name:", pet.name)
                print("Owner name:", pet.ownerName)


pet = Pets()

pet.addPets('04/13/2021', 'Pinky', 'David Smith')
pet.addPets('07/10/2020', 'Charlie', 'Joe Davis')
pet.addPets('12/22/2018', 'Teddy', 'Carl Johnson')
pet.addPets('07/10/2020', 'Kenny', 'Susan Jones')
pet.addPets('04/13/2021', 'Max', 'Bryan Miller')
pet.addPets('07/10/2020', 'Buddy', 'Kathy Brown')
pet.printPets()

【讨论】：

添加__lt__ 而不添加__eq__ 不是解决方案。