molar mass calculator

chemistry.py

import csv
import urllib

import os.path
if not os.path.isfile('periodictabledump.csv'):
    print "file doesn't exist yet...retrieved from Internet"
    url = "http://akiscode.com/project_files/pt/periodictabledump.csv"
    urllib.urlretrieve(url, "periodictabledump.csv")

with open('periodictabledump.csv') as csvfile:
  readCSV = csv.reader(csvfile, delimiter = ',')
  molar_masses=[]
  elements=[]
  for row in readCSV:
    molar_mass = row[1]
    element = row[3]

    molar_masses.append(molar_mass)
    elements.append(element)

  # print(molar_masses)
  # print(elements)

print "write the abbreviation of the element name and capitalize the first letter."
whatElement = raw_input("What element do you wish to know the molar mass of?")
elemdex = elements.index(whatElement)
theMass = float(molar_masses[elemdex])
newTotal = float(molar_masses[elemdex])
print 'The molar mass of',whatElement, 'is:',theMass
print "What do you wish to do now?"
print """
    [A] I want to add this given molar mass to the molar mass of another element
    [B] I want to multiply this given molar mass by some number
    [C] I want to find the molar mass of a new element
    [D] I wish to exit
    """
choice = ""
while choice != "D" or choice == "A" or choice == "B" or choice == "C":
    choice = raw_input("Enter the letter of your choice:")
    if choice == "A":
        whatElementadd = raw_input("Which element's molar mass do you want to add?")
        elemdex = elements.index(whatElementadd)
        theMassadd = ((float(molar_masses[elemdex])) + newTotal)
        newTotal = ((float(molar_masses[elemdex])) + newTotal)
        print 'The total molar mass is:', newTotal
    elif choice == "B":
        multiplied = int(raw_input("What number do you want to multiply the element's molar mass by?"))
        multipliedelementmass = multiplied * newTotal
        newTotal = multipliedelementmass = multiplied * newTotal
        print 'The total molar mass is:', multipliedelementmass

    elif choice == "C":
        newElement = raw_input("What new element do you wish to know the molar mass of?")
        elemdex = elements.index(newElement)
        theMassnewMass = float(molar_masses[elemdex])
        print 'The molar mass of', newElement, 'is:', theMassnewMass
    elif choice == "D":
        input("Press 'Enter' to confirm that you wish to exit.")

    else:
        print("You inputted an invalid command.")

    print "What do you wish to do now?"
    print """
        [A] I want to add the molar mass of this element to the molar mass of another element
        [B] I want to multiply the molar mass of this element by some number
        [C] I want to find the molar mass of a new element
        [D] I wish to exit
        """




input("Enter to exit")

# csv file from http://akiscode.com/getarticle.php?id=10


# with open('periodictabledump.csv') as csvfile:
#   readCSV = csv.reader(csvfile, delimiter = ',')
#   for row in readCSV:
#       print row[0] + " - " + row[2]
#       print "\tMolar Mass: %s" % row[1]
#       print "\tSymbol: %s" % row[3]
#       print "\n"
#       # print row[3] + ' = ' + row[1] #prints element name equal to its molar mass