python中字典的问题

Posted 2023-02-24

字典已经建好了，键也好了，怎么从键盘输入值然后加入键中？

参考技术A a = input()
this_dict =
this_dict["key"] = a

在腌制字典中检索单个对象的问题（Python 3）

【中文标题】在腌制字典中检索单个对象的问题（Python 3）

【英文标题】：Problem retrieving individual objects in pickled dictionary (Python 3)

【发布时间】：2019-12-13 16:57:18

【问题描述】：

我的程序将“食物”对象存储在字典中并存储在 csv 文件中，该文件充当数据库。我想根据命令从字典中检索单个食物对象，但是当我尝试时，我似乎只检索字典中的最后一个对象。

import pickle

class Food(object):
  fooddict = dict()

  def __init__(self, name, weight, calories, time):
    self.name = name
    self.weight = weight
    self.calories = calories
    self.time = time

  def __str__(self):
    return 'self.names'.format(self=self) + \
           ' weigh self.weight'.format(self=self) + \
           ' ounces, contain self.calories'.format(self=self) + \
           ' calories, and stay fresh for self.time'.format(self=self) + \
           ' days.'

  @classmethod
  def createFoodInput(cls):
    name = str(input("Enter the name: "))
    weight = float(input("Enter the weight: "))
    calories = float(input("Enter the calories: "))
    time = float(input("Enter how many days it can store for: "))
    return cls(name, weight, calories, time)

  def storeFoodDict(f):
    fooddict = Food.retreiveFoodDict()
    if fooddict == "Empty File":
        fooddict = dict(f.name: f)
        with open("food.csv", 'wb') as filewriter:
            try:
                pickle.dump(fooddict, filewriter)
            except:
                print("Error storing pickled dictionary")
    else:
        food_found = False
        for key in list(fooddict):
            if key.__eq__(f.name):
                print("Food already stored!")
                food_found = True
        if not food_found:
            fooddict.update(f.name: f)
            with open("food.csv", 'wb') as filewriter:
                try:
                    pickle.dump(fooddict, filewriter)
                except:
                    print("Error storing pickled dictionary")
  @classmethod
  def retreiveFoodDict(cls):
    with open("food.csv", 'rb') as filereader:
        try:
            fooddict = pickle.load(filereader)
            return fooddict
        except EOFError:
            return("Empty File")

def findFood(title):
fooddict = Food.retreiveFoodDict()
for key in list(fooddict):
   if key.__eq__(title):
        continue
return fooddict[key]

s = "apple"
n = findFood(s)           #does not work, it returns banana instead of apple
                          #which is really just grabbing whatever is the 
                          #last object in the dictionary

m = findFood("banana")    #seems to work, but only because banana is the
                          #last object in the dictionary

print(n) #should print an apple "food object" but instead prints a banana

print(str(m.calories)) #works, but if I said n.calories it would still print
                       #m.calories instead
p = Food.retreiveFoodDict() #seems to work and retrieve the dictionary
print(str(p))               #also seems to work of course

控制台输出： 香蕉重 5.0 盎司，含有 120.0 卡路里，可保鲜 3.0 天。 120.0 'apple': ma​​in.Food object at 0x00D2C2E0>, 'banana': ma​​in.Food object at 0x00D36D00>

字典包含 2 个食物对象（苹果和香蕉），但 print(n) 语句显示的是香蕉，而不是苹果。谁能指出这是为什么或我误解了什么？非常感谢！

【问题讨论】：

你为什么要腌制然后放入 csv，而不是只挑选整个东西？

似乎类的格式和输出搞砸了，但你可以edit 修复它。如果需要，请参阅code formatting help。顺便说一句，欢迎来到 Stack Overflow！查看tour。另外顺便说一句，您应该创建一个minimal reproducible example。

Shelve你的果实！

腌制整件事是什么意思？每次我在字典中存储一个新对象时，我都会尝试腌制整个字典，这是我的数据库。

【参考方案1】：

我找到了自己问题的答案。我在 findFood 函数中滥用了 continue 。 这段代码解决了我的问题。

def getFood(food_name):
    fooddict = Food.retreiveFoodDict()
        for key in list(fooddict):
           if key.__eq__(food_name):
               return fooddict[key]

此函数所做的只是在 csv 文件中检索对象字典并遍历键，直到找到传递的键名。如果找到，正确的键名将作为食物对象返回。我最初的错误是使用“继续”关键字来停止 for 循环，它直接在我们想要的对象之后返回对象。