In Python, lists are mutable, which means their contents (items) can be changed after creation. You can:

• Change individual items
• Change multiple items using slicing
• Increase or decrease list size during replacement
• Use loops or conditions to modify values

1. Change a Single Item in a List

Use the index to replace a specific item.

Example:

fruits = ["apple", "banana", "cherry"]
fruits[1] = "mango"
print(fruits)

Output:

['apple', 'mango', 'cherry']

Indexing starts at 0.

2. Change Multiple Items (Using Slicing)

You can change several items at once using slicing.

Example:

fruits = ["apple", "banana", "cherry", "orange"]
fruits[1:3] = ["kiwi", "pineapple"]
print(fruits)

Output:

['apple', 'kiwi', 'pineapple', 'orange']

3. Replace with Fewer Items Than Selected

You can shrink the list by replacing more items with fewer.

Example:

fruits = ["apple", "banana", "cherry", "orange"]
fruits[1:3] = ["grape"]
print(fruits)

Output:

['apple', 'grape', 'orange']

4. Replace with More Items Than Selected

You can increase the list size if you assign more values than selected.

Example:

fruits = ["apple", "banana", "cherry"]
fruits[1:2] = ["blackberry", "pear", "kiwi"]
print(fruits)

Output:

['apple', 'blackberry', 'pear', 'kiwi', 'cherry']

5. Replace All Items in a List

To completely overwrite the contents of a list:

Example:

fruits = ["apple", "banana", "cherry"]
fruits[:] = ["orange", "mango", "kiwi"]
print(fruits)

Output:

['orange', 'mango', 'kiwi']

6. Use a Loop to Modify Items

You can apply transformations to all elements using a loop.

Example: Multiply all elements by 2

numbers = [1, 2, 3, 4, 5]
for i in range(len(numbers)):
   numbers[i] *= 2
print(numbers)

Output:

[2, 4, 6, 8, 10]

7. Conditional Changes in a Loop

Modify list items based on conditions.

Example: Replace odd numbers with "odd"

numbers = [1, 2, 3, 4, 5]
for i in range(len(numbers)):
   if numbers[i] % 2 != 0:
       numbers[i] = "odd"
print(numbers)

Output:

['odd', 2, 'odd', 4, 'odd']

8. Change Nested List Items

Python lists can contain other lists (nested lists), and you can access and modify them too.

Example:

nested = [["a", "b"], ["c", "d"]]
nested[1][0] = "x"
print(nested)

Output:

[['a', 'b'], ['x', 'd']]

⚠️ Common Mistakes to Avoid

Correct Way:

fruits[1:3] = ["kiwi"]

Summary

• Use indexing (list[i]) to change individual items
• Use slicing (list[start:end]) for multiple items
• Replacing can change the size of the list
• You can also use loops and conditions to modify values
• Be careful when replacing using a string—it behaves like a list of characters