finding and replacing elements in a list

Question

I have to search through a list and replace all occurrences of one element with another. So far my attempts in code are getting me nowhere, what is the best way to do this?<

Answer 1

Here's a cool and scalable design pattern that runs in O(n) time ...

a = [1,2,3,4,5,6,7,6,5,4,3,2,1]

replacements = {
    1: 10,
    2: 20,
    3: 30,
}

a = [replacements.get(x, x) for x in a]

print(a)
# Returns [10, 20, 30, 4, 5, 6, 7, 6, 5, 4, 30, 20, 10]