element = {} string = {} string[0] = 'Li' string[1] = 'Cs' string[2] = 'H_' string[3] = 'P-' string[4] = 'CA' string[5] = 'N_' string[6] = 'H_' element[0] = 'H_' element[1] = 'He' element[2] = 'Li' element[3] = 'Be' element[4] = 'B_' element[5] = 'C_' element[6] = 'N_' element[7] = 'O_' element[8] = 'F_' element[9] = 'Ne' element[10] = 'Na' element[11] = 'Mg' element[12] = 'Al' element[13] = 'Si' element[14] = 'P_' element[15] = 'S_' element[16] = 'Cl' element[17] = 'Ar' element[18] = 'K_' element[19] = 'Ca' ptval = {} ptval['H_'] = '001' ptval['He'] = '002' ptval['Li'] = '003' ptval['Be'] = '004' ptval['B_'] = '005' ptval['C_'] = '006' ptval['N_'] = '007' ptval['O_'] = '008' ptval['F_'] = '009' ptval['Ne'] = '010' ptval['Na'] = '010' ptval['Mg'] = '011' ptval['Al'] = '012' ptval['Si'] = '013' ptval['P_'] = '014' ptval['S_'] = '015' ptval['Cl'] = '016' ptval['Ar'] = '017' ptval['K_'] = '018' ptval['Ca'] = '019' for element in string: if element in ptval.keys(): print ptval[element]