相对分子质量计算器

#A dictionary of some common elements and their relative atomic masses

elements = {'H': 1.008, 'He': 4.003, 'Li': 6.941, 'Be': 9.012, 

            'B': 10.81, 'C': 12.01, 'N': 14.01, 'O': 16.00, 

            'F': 19.00, 'Ne': 20.18, 'Na': 22.99, 'Mg': 24.31, 

            'Al': 26.98, 'Si': 28.09, 'P': 30.97, 'S': 32.07, 

            'Cl': 35.45, 'K': 39.10, 'Ar': 39.95, 'Ca': 40.08, 

            'Sc': 44.96, 'Ti': 47.87, 'V': 50.94, 'Cr': 52.00, 

            'Mn': 54.94, 'Fe': 55.85, 'Ni': 58.69, 'Co': 58.93, 

            'Cu': 63.55, 'Zn': 65.38, 'Ga': 69.72, 'Ge': 72.63, 

            'As': 74.92, 'Se': 78.96, 'Br': 79.90, 'Kr': 83.80, 

            'Rb': 85.47, 'Sr': 87.62, 'Y': 88.91, 'Zr': 91.22, 

            'Nb': 92.91, 'Mo': 95.94, 'Tc': 98.00, 'Ru': 101.1, 

            'Rh': 102.9, 'Pd': 106.4, 'Ag': 107.9, 'Cd': 112.4, 

            'In': 114.8, 'Sn': 118.7, 'Sb': 121.8, 'I': 126.9, 

            'Te': 127.6, 'Xe': 131.3, 'Cs': 132.9, 'Ba': 137.3, 

            'La': 138.9, 'Ce': 140.1, 'Pr': 140.9, 'Nd': 144.2, 

            'Pm': 145.0, 'Sm': 150.4, 'Eu': 152.0, 'Gd': 157.3, 

            'Tb': 158.9, 'Dy': 162.5, 'Ho': 164.9, 'Er': 167.3, 

            'Tm': 168.9, 'Yb': 173.0, 'Lu': 175.0, 'Hf': 178.5, 

            'Ta': 180.9, 'W': 183.8, 'Re': 186.2, 'Os': 190.2, 

            'Ir': 192.2, 'Pt': 195.1, 'Au': 197.0, 'Hg': 200.6, 

            'Tl': 204.4, 'Pb': 207.2, 'Bi': 208.9, 'Th': 232.0, 

            'Pa': 231.0, 'U': 238.0, 'Np': 237.0, 'Pu': 244.0, 

            'Am': 243.0, 'Cm': 247.0, 'Bk': 247.0, 'Cf': 251.0, 

            'Es': 252.0, 'Fm': 257.0, 'Md': 258.0, 'No': 259.0, 

            'Lr': 262.0, 'Rf': 267.0, 'Db': 270.0, 'Sg': 271.0, 

            'Bh': 270.0, 'Hs': 277.0, 'Mt': 276.0, 'Ds': 281.0, 

            'Rg': 280.0, 'Cn': 285.0, 'Nh': 284.0, 'Fl': 289.0, 

            'Mc': 288.0, 'Lv': 293.0}

# A function to calculate the relative molecular mass of a chemical formula

def calculate_rmm(formula):

    # Initialize the result to zero

    result = 0

    # Initialize an empty string to store the current element symbol

    element = ""

    # Initialize an empty string to store the current number of atoms

    number = ""

    # Initialize an empty list to store the stack of parentheses

    stack = []

    # Loop through each character in the formula

    for char in formula:

        # If the character is an uppercase letter

        if char.isupper():

            # If there is a previous element symbol

            if element:

                # If there is a previous number of atoms

                if number:

                    # Convert the number to an integer and multiply it by the relative atomic mass of the element

                    value = int(number) * elements[element]

                else:

                    # Otherwise assume the number is one and multiply it by the relative atomic mass of the element

                    value = elements[element]

                # If there is a stack of parentheses 

                if stack: 

                    # Append the value to the stack 

                    stack.append(value) 

                else: 

                    # Otherwise add it to the result 

                    result += value 

                # Reset the number to an empty string 

                number = "" 

            # Set the current element symbol to the character 

            element = char 

        # If the character is a lowercase letter 

        elif char.islower(): 

            # Append it to the current element symbol 

            element += char  

        elif char.isdigit():  

            number += char  

        elif char == "(":

            if element:  

                if number:  

                    value = int(number) * elements[element]  

                else:  

                    value = elements[element]  

                if stack:  

                    stack.append(value)  

                else:  

                    result += value   

                element = ""   

                number = ""   

            stack.append(char)   

        elif char == ")":

            if element:

                if number:

                    value = int(number) * elements[element]

                else:

                    value = elements[element]

                if stack:

                    stack.append(value)

                else:

                    result += value

            element = ""

            number = ""

            # Pop the values from the stack until reaching a left parenthesis

            temp_result = 0

            while stack and stack[-1] != "(":

                temp_result += stack.pop()

            # Pop the left parenthesis from the stack

            if stack and stack[-1] == "(":

                stack.pop()

            # Check if there is a number after the right parenthesis

            i = formula.index(char) + 1

            if i < len(formula) and formula[i].isdigit():

                # Multiply the temporary result by the number and append it to the stack or add it to the result

                temp_result *= int(formula[i])

                if stack:

                    stack.append(temp_result)

                else:

                    result += temp_result

                # Skip the next character as it is already processed

                continue

            else:

                # Otherwise append the temporary result to the stack or add it to the result as it is

                if stack:

                    stack.append(temp_result)

                else:

                    result += temp_result

    # Check if there is a remaining element and number at the end of the formula and add them to the result        

    if element:  

        if number:  

            value = int(number) * elements[element]  

        else:  

            value = elements[element]  

        result += value   

    return result

# Ask for user input and print out the result or error message  

def main():

    while True:

        try:  

            formula = input("Enter a chemical formula: ")

            rmm = calculate_rmm(formula)

            print("The relative molecular mass of {} is {:.3f}".format(formula,rmm))

        except KeyError as e:

            print("Unknown element: {}".format(e))

        except ValueError as e:

            print(e)

if __name__ == "__main__":

    main()