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# Python | Convert case of elements in a list of strings

Given a list of strings, write a Python program to convert all strings from lowercase/uppercase to uppercase/lowercase.

```Input : ['GeEk', 'FOR', 'gEEKS']
Output: ['geek', 'for', 'geeks']

Input : ['fun', 'Foo', 'BaR']
Output: ['FUN', 'FOO', 'BAR']```

Method #1: Convert Uppercase to Lowercase using map function

## Python3

 `# Python code to convert all string` `# from uppercase to lowercase.`   `# Using map function` `out ``=` `map``(``lambda` `x:x.lower(), [``'GeEk'``, ``'FOR'``, ``'gEEKS'``])`   `# Converting it into list` `output ``=` `list``(out)`   `# printing output` `print``(output)`

Output:

`['geek', 'for', 'geeks']`

Time complexity: O(n), where n is the length of the input list.
Auxiliary space: O(n), where n is the length of the output list.

Method #2: Convert Lowercase to Uppercase using List comprehension

## Python3

 `# Python code to convert all string` `# from uppercase to lowercase.`   `# Initialisation` `input` `=` `[``'fun'``, ``'Foo'``, ``'BaR'``]`   `# Converting` `lst ``=` `[x.upper() ``for` `x ``in` `input``]`   `# printing output` `print``(lst)`

Output:

`['FUN', 'FOO', 'BAR']`

Time complexity: O(n), where n is the number of elements in the input list.
Auxiliary space: O(n), where n is the number of elements in the input list, as a new list is created to store the converted strings.

Method #3: Using enumerate function

## Python3

 `lst ``=` `[``'Foo'``, ``'fOO'``, ``'geeKs'``]` `lst ``=` `[i.lower() ``for` `a,i ``in` `enumerate``(lst)]` `print``(lst)`

Output

`['foo', 'foo', 'geeks']`

Time complexity: O(n), where n is the length of the list.
Auxiliary space: O(n), as a new list is created to store the lowercase version of each string in the original list.

Method #4: Using casefold()

The approach is to use the str.casefold() method. This method is similar to the str.lower() method, but it is more aggressive in converting the string to a lowercase representation. It is particularly useful for handling case conversions involving non-ASCII characters, such as those found in the German language.

Here is an example of using str.casefold() to convert a list of strings to lowercase:

## Python3

 `input` `=` `[``'GeEk'``, ``'FOR'``, ``'gEEKS'``]` `output ``=` `[s.casefold() ``for` `s ``in` `input``]` `print``(output)` `# Output: ['geek', 'for', 'geeks']` `#This code is contributed by Edula Vinay Kumar Reddy`

Output

`['geek', 'for', 'geeks']`

Time complexity: O(n), where n is the length of the input list.
Auxiliary space: O(n), where n is the length of the output list.

Method 5: Using the lower()

## Python3

 `input` `=` `[``'fun'``, ``'Foo'``, ``'BaR'``]`   `lst ``=` `[x.lower() ``for` `x ``in` `input``]`   `print``(lst)`

Output

`['fun', 'foo', 'bar']`

Time Complexity: O(n)

Auxiliary Space: O(n), where n is length of list.

Method #6: Using a for loop

Convert uppercase letters to lowercase by using a for loop to iterate through each character in the string, and then using the lower() function to convert the uppercase letter to lowercase.

## Python3

 `# Python code to convert all string` `# from uppercase to lowercase.`   `# Using a for loop` `string ``=` `'GeEk FOR gEEKS'` `output ``=` `''` `for` `char ``in` `string:` `    ``if` `char.isupper():` `        ``output ``+``=` `char.lower()` `    ``else``:` `        ``output ``+``=` `char`   `# printing output` `print``(output)`

Output

`geek for geeks`

Time complexity: O(n), where n is the length of the input string. This is because the for loop iterates through each character in the string exactly once.

Auxiliary space: O(n), as we are creating a new string (output) to store the lowercase version of the input string.

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