LM FOR Loop in lists

Why Use For-Loops with Lists?

For-loops are extremely useful when working with lists, because they allow you to access each element in a structured and readable way. Unlike range()-based loops that use index numbers, direct iteration is often simpler and less error-prone.

Looping Through a List

You can loop directly over the elements of a list:

letters = ["A", "B", "C", "D"]
for element in letters:
    print(element)

Output:

A
B
C
D

Each item in the list letters is accessed one by one using the loop variable element.

Modify List Elements by Index

To change list elements, you need to access them by index. You can use range(len(...)) to loop through the indexes:

letters = ["A", "B", "C", "D"]
for i in range(len(letters)):
    letters[i] = letters[i] + "x"
print(letters)

Output:

['Ax', 'Bx', 'Cx', 'Dx']

Creating a New List from an Existing One

If you want to create a new list based on modifications of another list:

a = ["A", "B", "C", "A", "B", "A", "A"]
test = []  # this is an empty list

for i in range(len(a)):
    test.append(a[i].lower())

print(test)

Output:

['a', 'b', 'c', 'a', 'b', 'a', 'a']

Summary

  • Use for element in list for clean and direct access to each value.
  • Use for i in range(len(list)) if you need to modify items by index.
  • Lists are mutable, meaning their content can be changed.

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