Python 初学者 - 如何从列表中召回已删除的项目

Question

我是一个python初学者，我想知道一旦列表中的项目被替换，它能被召回吗？

Friends=["Jen","Lam","Sam","Song"]
print (Friends)

#replace a list item 
Friends[0] = "Ken"
print (Friends)

如果我想说 Jen 在 python 中被 Ken 替换而不是直接写出print("Jen")并使用变量，我应该如何写这行。

Answer 1

在替换之前跟踪Friends[0] 。

IE

friends=["Jen","Lam","Sam","Song"]
print(Friends)
replaced = friends[0]
friends[0] = "Ken"
print(replaced + " was replaced by " + friends[0])

您还可以使用pop和insert 。

friends=["Jen","Lam","Sam","Song"]
print(friends)
replaced = friends.pop(0)
friends.insert(0, "Ken")
print(replaced + " was replaced by " + friends[0])

Answer 2

从来没听说过。 但是您可以制作一份列表的副本，然后通过从该列表中获取旧名称来使用它来将其改回原来的状态。

Friends=["Jen","Lam","Sam","Song"]
replaceName = Friends[0]
newName= "ken"
Friends [0] = newName

print(replaceName, " was replaced by ", newName)
print(Friends)

Answer 3

如果您想用列表中的“ken”替换名称，则必须将“jen”存储为变量。 像这样的东西：

replace = Friends[0]
Friends[0] = "ken"

在这两行之后，当您打印(Friends[0]) 时，它会返回“Ken”，但您可以打印(replace) 并打印“jen”

您还可以使用其他列表方法将 Ken .append 到列表中以在列表中包含两个名称。 该站点对所有不同的列表方法以及如何使用它们都非常有帮助！ https://docs.python.org/3.9/tutorial/datastructures.html#the-del-statement

Answer 4

将“Jen”放在一个单独的变量中。

顺便说一下，我也是初学者:)

Answer 5

Friends = ["Jen", "Lam", "Sam", "Song"]

friend_to_delete = Friends[0]

print (Friends)

Friends[0] = "Ken"

print (Friends)

print(friend_to_delete, 'was replaced by', Friends[0])

Answer 6

非常简单的答案：

    Friends=['Jen', 'Lam', 'Sam', 'Song']                                     
    print (Friends)
    Friends.append('Ken') #This adds in the string('Ken') without directly altering the list
    Friends.reverse() #This reverses the order in your list
    Friends.remove('Jen') #This removes the string ('Jen') from your list

#Note you can also use Friends.pop(4) to remove the string 'Jen' since its reversed
    
print(Friends)