[Tutor] string indexing

[rahmad akbar]

hey guys, super  noob here, i am trying to understand the following code
from google tutorial which i failed to comprehend

#code start
# 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):
  # +++your code here+++
  # LAB(begin solution)
  n = s.find('not')
  b = s.find('bad')
  if n != -1 and b != -1 and b > n:
    s = s[:n] + 'good' + s[b+3:]
  return s
#code end

 on the following lines, what is -1, is that index number? and i dont
understand the entire second line

if n != -1 and b != -1 and b > n:
    s = s[:n] + 'good' + s[b+3:]

-- 
many thanks
mat
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