def rfind(self, sub ,start = 0 ,end = sys.maxsize):
'''S.rfind(sub [,start [,end]]) -> int
Return the highest index in S where substring sub is found,
such that sub is contained within S[start:end]. Optional
arguments start and end are interpreted as in slice notation.
Return -1 on failure.
'''
string = self[start:end]
# corner cases
if string == '':
return 0 if sub == '' else -1
if sub == '':
return len(string)+start
c = 0
it = StringSearch(sub,self,self._factory.collator)
it.setAttribute(USearchAttribute.OVERLAP,False)
r = it.last()
while r>= 0:
match = it.getMatchedText()
if self.__class__(match) == self.__class__(sub):
return start + r
r = it.preceding(r)
return r
