':param key: a string with length of [0, 32]'

def delete(self, key):

    if (not is_string(key)):
        raise Exception('Key    must    be    string')
    if (len(key) > 32):
        raise Exception('Max    key    length    is    32')
    old_root = copy.deepcopy(self.root_node)
    self.root_node = self._delete_and_delete_storage(self.root_node, bin_to_nibbles(to_string(key)))
    self.replace_root_hash(old_root, self.root_node)
