If we use
end as given, then the new combined string will contain the letter at index
end, which we do not want. We need to exclude all the characters between start and end, including the characters at those indices, hence,
end + 1.
Sketch it out on paper to give yourself a better picture.
['abcdefg'][start ('h') 'ijklmnopqr' end('s')]['tuvwxyz'] .. 6 7 16 17 ..
Recall that a slice excludes the stop index so when we write,
str[:7] it gives
abcdefg, and when we write,
str[17:] it gives
The removed substring should be 10 characters long,
len('hijklmnpqr') # 10