docs: def remove_ngram(self, ngram):
          """
          Removes a given ngram from the databae. The ngram has to be in the
          database, otherwise this method will stop with an error.
  
          Parameters
          ----------
          ngram : iterable of str
              A list, set or tuple of strings.
  
          """
          query = "DELETE FROM _{0}_gram".format(len(ngram))
          query += self._build_where_clause(ngram)
          query += ";"
          self.execute_sql(query)