Python problem, help please?

So, as a starter, this would be just a basic problem that I am not able to solve.

Here is the problem:

# E. not_bad

# Given a string, find the first appearance of the

# substring 'not' and 'bad'. If the 'bad' follows

# the 'not', replace the whole 'not'...'bad' substring

# with 'good'.

# Return the resulting string.

# So 'This dinner is not that bad!' yields:

# This dinner is good!

def not_bad(s):

return

I am thinking that it should be solved using len function for finding not and bad, so I used it and then when I put this command - s.replace(a to b,'good')

It's giving me an error for this one and I don't think that this would work 'cuz in the problem it has given that erase the whole part from not to bad.

I've been working on that problem since 1 week! But no luck solving it, so those of you masters out there, please tell me a solution.

Also, if you are wondering how I got this len idea is 'cuz of this problem:

# B. both_ends

# Given a string s, return a string made of the first 2

# and the last 2 chars of the original string,

# so 'spring' yields 'spng'. However, if the string length

# is less than 2, return instead the empty string.

def both_ends(s):

a = len(s)

if a < 2:

print

else:

print s[0] , s[-2]

return

A fast response will really be appreciated

I did put this topic in altergaming, but didn't get any response yet. So posting it here hoping to get a quick response