code: def get_group(self, t, i):
          
  
          try:
              value = []
              if t in _DIGIT and t != '0':
                  value.append(t)
                  t = next(i)
                  if t in _DIGIT:
                      value.append(t)
                  else:
                      i.rewind(1)
          except StopIteration:
              pass
          return ''.join(value) if value else None
docs: Get group number.