import csv

def read_table(a_file, a_dict):
    """Read Periodic Table file into a dict. with element symbol as key.
        periodic_file is a file object opened for reading """
    data_reader = csv.reader(a_file)

    for row in data_reader:
        # ignore header rows: elements begin with a number
        if row[0].isdigit():  
            symbol_str = row[1]
            a_dict[symbol_str] = row[:8]  # ignore end of row
        
def parse_element(element_str):
    """Parse element string into symbol and quantity,
       e.g. Si2 returns ('Si',2)"""
    symbol_str=""
    quantity_str = ""
    for ch in element_str:
        if ch.isalpha():
            symbol_str = symbol_str + ch
        else:
            quantity_str = quantity_str + ch
    if quantity_str == "":                  # if no number, default is 1
        quantity_str = "1"
    return symbol_str, int(quantity_str)

# 1. Read File
periodic_file = open("Periodic-Table.csv", "r",encoding="windows-1252")

# 2. Create Dictionary of Periodic Table using element symbols as keys
periodic_dict={}
read_table(periodic_file, periodic_dict)

# 3. Prompt for input and convert compound into a list of elements
compound_str = input("Input a chemical compound, hyphenated, e.g. C-O2: ")
compound_list = compound_str.split("-")


# 4. Initialize atomic mass
mass_float = 0.0
print("The compound is composed of: ", end=' ')

# 5. Parse compound list into symbol-quantity pairs, print name, and add mass
for c in compound_list:
    symbol_str, quantity_int = parse_element(c)
    print(periodic_dict[symbol_str][5], end=' ')  # print element name
    mass_float = mass_float + quantity_int *\
                 float(periodic_dict[symbol_str][6]) # add atomic mass

print("\n\nThe atomic mass of the compound is", mass_float)

periodic_file.close()