Often in Python, you may need to clean several lists of strings using the same operations inside a loop and save the results as permanently updated lists. You don’t need to keep the original lists — just store the cleaned versions separately.

For example, suppose you have the following lists of messy strings with extra spaces around the words:

List_A = [" Apple ", "banana ", " Cherry"]
List_B = [" Grape", "orange ", " PEAR "]

And suppose you want to remove the extra spaces around each word and convert all words to lowercase.

You can achieve this using the following solutions:

# Solution 1: The results are stored as separate cleaned lists.

List_A = [" Apple ", "banana ", " Cherry"]
List_B = [" Grape", "orange ", " PEAR "]

Lists = [List_A, List_B]

cleaned_lists = [[s.strip().lower() for s in list] for list in Lists]

Then, unpack the results into separate lists or variable names

List_A, List_B = cleaned_lists  # Unpack to get seperate names

Now print both lists to see the permanenetly cleaned results.

print(List_A)

print(List_B)

Example 2: When you want to remove “x” from both lists and obtain permanently cleaned Lists.

import re

# Example messy lists
List1 = ['myoxcardial', 'anoxemia', 'dixabetes']
List2 = ['exzema', 'xdata', 'myoxpathy']

Lists = [List1, List2]

for list in Lists:
    list[:] = [re.sub('x', ' ', i) for i in list]
    list[:] = set(list) 

Note that to modify the original lists, you should mutate them in place using slice assignment.

Let’s print out the cleaned lists:

print(List1)

print(List2)

Hope this tutorial helps! Read our other tutorials to learn more.