I'm trying to convert every string in a list to it's lowercase format using this function:

def lower_list(strings):
    for string in strings:
        string = string.lower()
    return strings

But this implementation is not working, however when using the range funtion and I iterate using an index:

def lower_list(strings):
    for i in range(len(strings)):
        strings[i] = strings[i].lower()
    return strings

I do get every element on my list converted to lowercase:

> print(lower_list(mylist))
['oh brother where art thou', 'hello dolly', 'monsters inc', 'fargo']

But with the first implementation I get the original list with Uppercase values, am I missing something important in how the for loop works?

CodePudding user response：

In the first case, all you are doing is storing the lowercase value in a variable, but the list is untouched. In the second case, you are actually updating the value in the list at that index.

You can also use a lambda function here:

def lower_list(strings):
    return list(map(lambda x: x.replace(x, x.lower()), strings))

List comprehension is the easiest and the best:

def lower_list(strings):
    return [string.lower() for string in strings]

CodePudding user response：

The reason the first one does not work is that it is not actually modifying the value inside of the list, rather it is just affecting a copy of the value in the list. When you use the index-based function, it modifies the list itself.

CodePudding user response：

def lower_list(strings):
    for string in strings:
        index_of_string = strings.index(string)
        string = string.lower()
        strings[index_of_string] = string
    return strings

If you want the first one to work, maybe you can try something like that, but thats a bad way of doing it, just showing it as an example so maybe you'll understand better. You need the index of that string so you can replace it in the list. In your first attempt, you do not replace anything in the list.