即使字典外的相同变量被更改，字典内的变量值也不会改变。为什么？

Question

我有一本字典 restaurants，想根据用户输入的日期更改 restaurants 中嵌套列表中 opening hours 和 closing hours 的值。

opening_time=0
closing_time=0

##snippet of the dictionary 
restaurants={"Macdonald's":\
             \
             [{"Monday":[700,2400],\
               "Tuesday":[700,2400],\
               "Wednesday":[700,2400],\
               "Thursday":[700,2400],\
               "Friday":[700,2400],\
               "Saturday":[700,2400],\
               "Sunday":[1000,2200]},\
              \
              "Block XXX, #01-XX",\
              "Fast food restaurant known for its all round excellent menu.",\
              \
              ["Breakfast",[opening_time,1100],\
               {"Egg McMuffin":"$1",\
                "Hotcakes":"$1",\
                "Big Breakfast":"$1"}],\
              ["Lunch/Dinner",[1100,closing_time],\
               {"Double Cheeseburger":"$3.20",\
                "McChicken":"$3.95",\
                "Big Mac":"$4.70",\
                "Chicken McNuggets (6pcs)":"$4.95",\
                "McWings":"$4.95"}],\
              ["All Day",[opening_time,closing_time],\
               {"Fillet-O-Fish":"$4.60",\
                "Corn Cup":"$1.95"}]]}

我希望代码循环并打印所有餐厅和菜单，同时指示所述餐厅和菜单在用户输入的时间是否可用。

for key in restaurants:  #key refers to restaurant name
    print("","",sep='\n')
    if day_now in restaurants.get(key)[0].keys():  #check if restaurant is open on that day
        opening_time=restaurants.get(key)[0][day_now][0]  #set opening and closing hours to those on that day
        closing_time=restaurants.get(key)[0][day_now][1]
        if time_now>=opening_time and time_now<closing_time:  #check if restaurant is open within that time period
            status="Open"
            open_restaurants.update(restaurants)
            print(key,"Status: "+status,"Opening Hours Today:"+str(opening_time)+" to "+str(closing_time),\
                  "Location: "+restaurants.get(key)[1],"Description: "+restaurants.get(key)[2],sep='\n')
            for i in range(3, len(restaurants.get(key))):  #goes through the menus the restaurant has
                print(restaurants.get(key)[i][1][0]) #prints 0
                print(restaurants.get(key)[i][1][1]) #prints 0
                if time_now>=restaurants.get(key)[i][1][0] and time_now<restaurants.get(key)[i][1][1]:  #check if menu have
                    print("")
                    print(restaurants.get(key)[i][0]+" Menu: Available","Item: Cost:",sep='\n')
                    for item in restaurants.get(key)[i][2].keys():
                        print(item, restaurants.get(key)[i][2][item],sep=' ')
                else:
                    print("")
                    print(restaurants.get(key)[i][0]+" Menu: Unavailable","Item: Cost:", sep='\n')
                    for item in restaurants.get(key)[i][2].keys():
                        print(item, restaurants.get(key)[i][2][item],sep=' ')            
        else:
            closed_restaurants.update(restaurants)
            status="Closed"
            print(key,"Status: "+status,"Opening Hours Today:"+str(opening_time)+" to "+str(closing_time),\
                  "Location: "+restaurants.get(key)[1],"Description: "+restaurants.get(key)[2], sep='\n')
    else:
        closed_restaurants.update(restaurants)
        status="Closed"
        print(key,"Status: "+status,"Opening Hours Today:"+str(opening_time)+" to "+str(closing_time),\
                  "Location: "+restaurants.get(key)[1],"Description: "+restaurants.get(key)[2], sep='\n')

print(opening_time) #prints the correct opening and closing hours
print(closing_time) 

但是，字典中的 opening hours 和 closing hours 变量无法在循环中分配给所需的值，并保持它们最初在循环外分配的状态。

直接打印变量名表示新值赋值成功。

有人可以帮我解决这个问题吗？谢谢。

Answer 1

让我们用这个简单的例子来说明你的假设是错误的：

var = 1
lst = [var]
var = 2
print(lst)

应该打印什么，[1] 或 [2]？它将打印[1]。您在这里拥有的不是变量引用列表，而是整数列表。你取了var 的值，并将其放入列表中。一份副本，如果你想要的话。

这个呢？

a = 1
b = a
a = 2

同样，b 在此之后仍然是 1。你把写在a的地方写的，放到b的地方。

你需要真正更新字典里面的值，更新opening_hours是不够的。