我正在尝试在python上制作一个货币计算器：
print("Please choose which currency you want to convert:")
print("A - Korean Won to US Dollar (Exchange Rate: 0.000905)")
print("B - Korean Won to Euro (Exchange Rate: 0.000807350908)")
print("C - Korean Won to Japanese Yen (Exchange Rate: 0.0919061643)")
print("D - Korean Won to Chinese RMB (Exchange Rate: 0.00603703605)")
print("E - Quit ")
A=0
B=0
C=0
D=0
usd = 0.000905
eur = 0.000807350908
yen = 0.0919061643
rmb = 0.00603703605
def main():
(option, amount) = Input()
Output(totalamount)
def Input():
option = eval(input("Enter your option: "))
amount = eval(input("Enter the amoutn in Korean Won: "))
if option == "A":
totalamount = (amount * usd)
print (amount +"Won equals to "+totalamount+" USD")
elif option== "B":
totalamount = (amount * eur)
print (amount +"Won equals to "+totalamount+" Euro")
elif option== "C":
totalamount = (amount * yen)
print (amount +"Won equals to "+totalamount+" Yen")
elif option== "D":
totalamount = (amount * rmb)
print (amount +"Won equals to "+totalamount+" Chinese RMB")
else:
quit
main()
我仍在学习如何使用python，但我想知道为什么每当我运行程序时都会收到此错误：
TypeError: cannot unpack non-iterable NoneType object
我该如何解决这个问题？
您不返回任何内容，并将输出None放在两个不同的变量中。这是不对的。 在功能添加的末尾
return option, amount
def main():
(option, amount) = Input()
Output(totalamount)
在这里，要分配option和amount变量的值应该由input((函数提供，但如您所见，您的输入函数在返回某个值的地方没有，因此默认情况下其返回None
您希望返回一些值。
这是您的完整代码
print("Please choose which currency you want to convert:")
print("A - Korean Won to US Dollar (Exchange Rate: 0.000905)")
print("B - Korean Won to Euro (Exchange Rate: 0.000807350908)")
print("C - Korean Won to Japanese Yen (Exchange Rate: 0.0919061643)")
print("D - Korean Won to Chinese RMB (Exchange Rate: 0.00603703605)")
print("E - Quit ")
A=0
B=0
C=0
D=0
usd = 0.000905
eur = 0.000807350908
yen = 0.0919061643
rmb = 0.00603703605
def main():
(option, amount,totalamount) = Input() #modified
print(totalamount)
def Input():
option = input("Enter your option: ")
amount = eval(input("Enter the amoutn in Korean Won: "))
totalamount=0 #added here
if option == "A":
totalamount = (amount * usd)
print (str(amount) +"Won equals to "+str(totalamount)+" USD")
elif option== "B":
totalamount = (amount * eur)
print ("{} Won equals to {} Euro".format(amount,totalamount))
elif option== "C":
totalamount = (amount * yen)
print ("{} Won equals to {} Yen".format(amount,totalamount))
elif option== "D":
totalamount = (amount * rmb)
print ("{} Won equals to {} Chinese RMB".format(amount,totalamount))
else:
quit
return option,amount,totalamount
main()
这里有一些建议/和修复。 还有很多东西可以改进，但我想展示一些基本的，希望它们不会太复杂而难以理解，但可以制作你的代码 更好。
这个想法是编写易于阅读和更改的代码。
usd = 0.000905
eur = 0.000807350908
yen = 0.0919061643
rmb = 0.00603703605
def print_choices():
"""
This is a doc string. Here you should describe what your function is doing.
This function prints the choices, that a user can make
"""
print("Please choose which currency you want to convert:")
# DRY: (=Don't Repeat Yourself). you have the exchange rate already in
# variables. so use them, so that if the exchange rate changes you
# need to change only one line in your code.
print("A - Korean Won to US Dollar (Exchange Rate: %f)" % usd)
print("B - Korean Won to Euro (Exchange Rate: %f)" % eur)
print("C - Korean Won to Japanese Yen (Exchange Rate: %f)" % yen)
print("D - Korean Won to Chinese RMB (Exchange Rate: %f)" % rmb)
print("E - Quit")
# describe what happens if you enter another value
# lateron you might want to rewrite your code such, that it rejects
# any option, that is not A, B, C, D, E and asks for input until it is
# correct.
print("any other input will Quit ")
# variables A,B,C,D are not used in your code, so remove them
# function names should only use lowercase characters and '_'
# This is a way of telling others, that this is a variable or a function
# It is got practice, that function names start with a verb and then an object.
def get_user_input():
"""
This function prompts the user for an option and an amount in
Korean Won and returns it to the caller.
returns: options, amount
"""
option = input("Enter your option: ")
# convert option to uppercase, so even if the user enters 'a',
# option 'A' will be chosen
option = option.upper()
# eval should not be used it is a dangerous function. Use float instead
amount = float(input("Enter the amount in Korean Won: "))
return option, amount
def calculate_and_print_converted_amount(option, amount):
"""
depending on option, amount is converted to another currency
This function calculates and displays the converted amount
and the currency.
If option "E" is selected Nothing is displayed.
if an unknown option is selected a small warning will be displayed
and no currency conversion is performed.
"""
if option == "A":
conversionrate = usd
currency = "USD"
elif option == "B":
conversionrate = eur
currency = "Euro"
elif option== "C":
conversionrate = yen
currency = "Yen"
elif option== "D":
conversionrate = rmb
currency = "Chinese RMB"
elif option== "E":
return
else:
# quit is no python command use return instead to return from
# a function.
# alternatively you can exit the entire python script
# with sys.exit()
print("unknown option %s. Will quit" % option)
return
# Use only one print statement, so you can change formatting by changin
# only one line
totalamount = amount * conversionrate
print ("%.2f Won equals to %.2f %s" % (amount, totalamount, currency))
def main():
print_choices()
(option, amount) = get_user_input()
calculate_and_print_converted_amount(option, amount)
# if you wanted to you could have one function (calculate_amount),
# that just calculates the amount and returns the amount and the
# currency and another function printing the answer.
# you see that many programs separate 'calculation' from 'presentation'
# one function does the work, the other one decides how to 'present'
# the information. (print to the terminal, write to a file, display
# with a GUI framework.
# If you'd separate code like that you could re use the calculation if
# you change your user interface and you just had to reimplement the
# function presenting the result
main()