实验室：计算折扣

Question

我正在做一个练习，到目前为止，代码（在其他线程的帮助下）运行得很好，但从数学角度来看，无法得到正确的结果

下面是代码：

#getting base prices from user
item1 = float(input('Enter the price of the first item: '))
item2 = float(input('Enter the price of the second item: '))
clubc = raw_input('Does customer have a club card? (Y/N): ')
tax = float(input('Enter tax rate, e.g. 5.5 for 5.5% tax: '))
basep = (item1 + item2)
print('Base price = ', basep)

#setting variables for calculation
addtax = (1 + (tax / 100))

#conditions for output
if item1 >= item2 and clubc == 'N':
    priceafterd = float(item1 + (item2 / 2))
    print('Price after discounts = ', priceafterd)
    totalprice = (priceafterd * addtax)
    print('Total price = ', totalprice)
elif item2 >= item1 and clubc == 'N':
    priceafterd = float(item2 + (item1 / 2))
    print('Price after discounts = ', priceafterd)
    totalprice = (priceafterd * addtax)
    print('Total price = ', totalprice)

if item1 >= item2 and clubc == 'Y':
    priceafterd = float((item1 + (item2 / 2)) * 0.9)
    print('Price after discounts = ', priceafterd)
    totalprice = (priceafterd * var3)
    print('Total price = ' + totalprice)
else:
    priceafterd = float((item2 + (item1 / 2)) * 0.9)
    print('Price after discounts = ', priceafterd)
    totalprice = (priceafterd * var3)
    print('Total price = ' + totalprice)

这个练习需要编写一个程序，根据促销活动、俱乐部卡和税收，计算客户购买两件商品后必须支付的金额

问题在于结果。作为输入示例：

Enter price of the first item: 10
Enter price of the second item: 20
Does customer have a club card? (Y/N): y
Enter tax rate, e.g. 5.5 for 5.5% tax: 8.25
Base price = 30.00
Price after discounts = 22.50
Total price = 24.36

相反，我得到了：

line 33, in <module>
print('Total price = ' + totalprice)
TypeError: cannot concatenate 'str' and 'float' objects

语法有什么问题？非常感谢

Answer 1

问题

在第二个条件中，您编写了print('Total price = ' + totalprice)行而不是print('Total price = ', totalprice)，问题在于：

totalprice有float类型，同时'Total price = '是str，您试图做的几乎就像str() + float()，因为python不知道如何连接字符串和浮点数，所以它引发了一个异常

如何解决

1） 到处使用相同的print('Total price = ', totalprice)行

Why does it work and print('Total price = ' + totalprice) does not?

因为print会自动将所有内容转换为字符串表示，所以您可以想象print('Total price = ', totalprice)表达式是这样的：

print(str('Total price = ') + " " + str(totalprice))

2） 将float转换为str并连接str

print('Total price = ' + str(totalprice))

str(totalprice)将totalprice从float转换为str，python知道如何将字符串连接在一起

3） 格式化

"Total price = {}".format(3.14)"相当于"Total price = 3.14"字符串，
所以print("Total price = {}".format(totalprice))也会起作用

在python 3中，我们还有f-Sting：

f"Total price = {3.14}" == "Total price = 3.14"

print(f"Total price = {totalprice}")