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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