Replace Values in a List in Python

Given a list of elements and a value to replace, the task is to update one or more matching values with a new value. For Example:

Input: a = [10, 20, 30, 40, 50] and Replace value 30 -> 99
Output: [10, 20, 99, 40, 50]

Using List Indexing

This method replaces a value by directly accessing a specific position in the list and assigning a new value to that position. It works when the index of the element to be replaced is already known.

[10, 20, 99, 40, 50]

Explanation:

• a[2] accesses the element at index 2
• = assigns the new value 99
• The list a is updated in place

Using List Comprehension

This method checks every element in the list and replaces only those values that satisfy a given condition, while rebuilding the list in a single expression using list comprehension.

[10, 20, 99, 40, 50]

Explanation:

• for x in a iterates over each element
• 99 if x == 30 else x replaces the value conditionally
• The updated elements are stored back in a

Using map() with lambda

This method goes through each element of the list and applies a small rule to it. The rule checks the value and replaces it only when the condition matches, otherwise the value remains the same.

[10, 20, 99, 40, 50]

Explanation:

• map() processes each element of a
• lambda x: 99 if x == 30 else x defines the replacement condition
• list() converts the result into a list

Using for Loop

This method walks through the list using index positions and replaces values whenever the specified condition is met during iteration with the help of for loop.

[10, 20, 99, 40, 50]

Explanation:

• range(len(a)) generates index values
• a[i] accesses elements using indexes
• Assignment updates the matching value in the list