我正在尝试使用 insert 方法在列表中已经存在的每个元素之后将相同的元素添加到我的列表中

Question

mylist = ['.','.','.']
for i in mylist:
    mylist.insert(i,'x')


print(mylist)

The problem is that I keep on getting the error message:

TypeError: 'str' object cannot be interpreted as an integer

I know of the join() method however I am trying to make it work so that the elements that i am adding can be manipulated later on.

Answer 1

When you do for i in mylist you get the actual list items in i , not their indexes. You then try to use insert - that functions requires an integer index (and is getting a string item instead). ( see here )

In addition to that, you're iterating over a list while also changing it's length, that's a bad practice and a recipe for a lot of bugs.

The correct way would be to create a new list entirely:

mylist = ['.','.','.']
new_list = []
for item in mylist:
    new_list.append(item)
    new_list.append('x')

Your new_list is now: ['.', 'x', '.', 'x', '.', 'x']

Answer 2

The issue is insert takes an int and string as a parameter.

When you write...

for i in myList:

You are taking i as the value in each position. Since the values in myList are strings, that's the error message you are seeing. Try instead:

for i in range(len(myList)):

This returns a list made up of the numbers starting from 0 and going to before len(myList). However, this also presents a problem. The list of positions is generated before the loop starts, so you have to be very careful since adding to the list doesn't change the number of interations. As such, the simplest implementation would be...

i = 1
while i < len(myList):
    myList.insert(i, 'x')
    i += 2

Answer 3

list.insert() method works with indices not the element themselves. When you are saying for i in mylist , you are iterating over the elements, which are strings, so you get the error you mentioned, as indices can not be str . First line of thinking should be to go by indices, but then again, if you modify the list while iterating over it, you will modify the list everytime you insert an element and hence will get unexpected results. And it is highly discouraged. Nevertheless, if you want to do so, here you go:

mylist = ['.','.','.']
for i in range(len(mylist)):
    mylist.insert(i+i+1,'x')

print(mylist)

Output:

['.', 'x', '.', 'x', '.', 'x']