Someone

array = {}
string = {}

string[0] = 'Li'
string[1] = 'Cs'
string[2] = 'H_'
string[3] = 'P-'
string[4] = 'CA'
string[5] = 'N_'
string[6] = 'H_'

array[0] = 'H_'
array[1] = 'He'
array[2] = 'Li'
array[3] = 'Be'
array[4] = 'B_'
array[5] = 'C_'
array[6] = 'N_'
array[7] = 'O_'
array[8] = 'F_'
array[9] = 'Ne'
array[10] = 'Na'
array[11] = 'Mg'
array[12] = 'Al'
array[13] = 'Si'
array[14] = 'P_'
array[15] = 'S_'
array[16] = 'Cl'
array[17] = 'Ar'
array[18] = 'K_'
array[19] = 'Ca'

for i,v in array.iteritems():
        for j,w in string.iteritems():
		if v == w
			print v