code: def append(self, val):
          
          new_len = self.length + len(val)
          to_add = new_len - len(self.bfr)
          if self.strict and to_add > 0:
              raise ValueError("Cannot resize buffer")
          self.bfr[self.length:new_len] = val
          self.length = new_len
docs: Append byte string val to buffer
          If the result exceeds the length of the buffer, behavior
          depends on whether instance was initialized as strict.
          In strict mode, a ValueError is raised.
          In non-strict mode, the buffer is extended as necessary.