code: def get_target_error(self,i):
      
      x = self._target_hpas[i]
      h = x['hpa']
      pos = x['pos']
      prob = 0
      be = BaseError('target')
      be.set_observable(h.get_target(),h.get_query())
      if i != 0 and pos == 0: # check for a total deletion before
        prev = x['prev-hpa']
        if len(prev.get_target()) == 0: # total insertion
          ilen = len(prev.get_query())
          be.set_unobserved_before(0,len(prev.get_query()),prev.get_query()[0],0.5)
      if i != len(self._target_hpas)-1 and pos == len(h.get_target())-1: # check for a total deletion before
        if x['next-hpa']:
          foll = x['next-hpa']
          if len(foll.get_target()) == 0: # total insertion
            be.set_unobserved_after(0,len(foll.get_query()),foll.get_query()[0],0.5)
      return be
docs: Just get a single error characterization based on the index relative to the target
  
      :param i: list index
      :type i: int
      :returns: base-wise error
      :rtype: HPA group description