code: def check(self, chemical_composition, reaction_energy):
          
          con = self.connection or self._connect()
          self._initialize(con)
          cur = con.cursor()
          statement = """SELECT reaction.id FROM reaction WHERE
          reaction.chemical_composition=? and reaction.reaction_energy=?"""
          argument = [chemical_composition, reaction_energy]
  
          cur.execute(statement, argument)
          rows = cur.fetchall()
          if len(rows) > 0:
              id = rows[0][0]
          else:
              id = None
          return id
docs: Check if entry with same surface and energy is allready written
          to database file
          Parameters
          ----------
          chemcial_composition: str
          reaction_energy: str
  
          Returns id or None