如何在 Python 中乘以小数
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/28522152/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to Multiply Decimals in Python
提问by matthewpg123
I was writing a pounds to dollars converter program. I encountered some problems multiplying the two numbers.
我正在写一个英镑到美元的转换器程序。我在将两个数字相乘时遇到了一些问题。
pounds = input('Number of Pounds: ')
convert = pounds * .56
print('Your amount of British pounds in US dollars is: $', convert)
Can anyone tell me the code to correct this program?
谁能告诉我纠正这个程序的代码？
回答by Maddy
def main():
pounds = float(input('Number of Pounds: '))
convert = pounds * .56
print('Your amount of British pounds in US dollars is: $', convert)
main()
If you are using input, you are inputing a string. You want to input a floating number for this questions.
如果您正在使用输入，则您正在输入一个字符串。您想为此问题输入一个浮点数。
回答by Sylvain Leroux
In Python 3 inputwill return a string. This is basically equivalent of raw_inputin Python 2. So, you need to convert that string to a number before performing any calculation. And be prepared for "bad input" (i.e: non-numeric values).
在 Python 3input中将返回一个字符串。这基本上等同raw_input于 Python 2。因此，您需要在执行任何计算之前将该字符串转换为数字。并为“错误输入”做好准备（即：非数字值）。
In addition, for monetary values, it is usually nota good idea to use floats. You should use decimalto avoid rounding errors:
此外，对于货币价值，使用浮点数通常不是一个好主意。您应该使用decimal以避免舍入错误：
>>> 100*.56
56.00000000000001
>>> Decimal('100')*Decimal('.56')
Decimal('56.00')
All of that lead to something likethat:
所有这些都会导致类似的事情：
import decimal
try:
pounds = decimal.Decimal(input('Number of Pounds: '))
convert = pounds * decimal.Decimal('.56')
print('Your amount of British pounds in US dollars is: $', convert)
except decimal.InvalidOperation:
print("Invalid input")
Producing:
生产：
sh$ python3 m.py
Number of Pounds: 100
Your amount of British pounds in US dollars is: $ 56.00
sh$ python3 m.py
Number of Pounds: douze
Invalid input
