Possible Bugs in substring program

I have written a small snippet to validate a substring in a string in O(n). I have tested the code using some combinations. I require your help to let me know if there are any bugs in my code with respect to any other cases that I might have missed out:-

class StringClass( object ):
    def __init__( self, s ):
        self._s = s
    def __contains__( self, s ):
        ind = 0
        for ch in self._s:
            if ind < len( s ) and ch == s[ind]:
                ind += 1
            elif ind >= len( s ):
                return True
            elif ch == s[0]:
                ind = 1
            elif ch != s[ind]:
                ind = 0

        if ind >= len( s ):
            return True

if __name__ == '__main__':
    s = StringClass( 'I llove bangaolove' )
    print 'love' in s

PS: Here, Instead of trying to find the string 'love' in 'I llove bangalove', I'm using the other method: i.e. to find if the string 'I llove bangalove' contains 'love'.

Please let me know if there are any corrections to be made here.