string - google python class strings2.py exercise E -
what happens @ line ? why -1 ?
if n != -1
e. not_bad given string, find first appearance of substring 'not' , 'bad'. if 'bad' follows 'not', replace whole 'not'...'bad' substring 'good'. return resulting string. 'this dinner not bad!' yields: dinner good!
def not_bad(s): n = s.find('not') b = s.find('bad') if n != -1 , b != -1 , b > n: s = s[:n] + 'good' + s[b+3:] return s
-1 means substring not found.
from official python documentation:
return lowest index in s substring sub found such sub wholly contained in s[start:end]. return -1 on failure. defaults start , end , interpretation of negative values same slices.
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