如何在 Python 中找到变量的百分比？

Question

我不知道如何在 Python 中找到变量的百分比。这是代码示例：

money =546.97
week=0
for i in range(10):
    money=money+16
    money=money+(5% money)
    print('you have',money,'dollars')
    week=week+4
    print(week)
i = i +1

它总是只加 21，因为它看到 5%，并给出等式（5% 的钱）的值为 5。

Answer 1

While the % symbol means "percent of" to us, it means an entirely different thing to Python.

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In Python, % is the modulo operator. Takes the thing on the left, divides it by the thing on the right, and returns the remainder of the division.

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>>> 9 % 4\n1\n>>> 9 % 3\n0\n

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So when you do 5% money, Python reads it as "divide 5 by money and return the remainder". That\'s not what you want at all!

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To answer the question, we need to look at what a percentage is. Percent comes from Latin per cent, meaning "per one hundred things". So "five percent" literally means "take five out of every hundred things." Okay, great! So what?

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So to find a percentage of a number, you must multiply that number by its decimal percentage value. 5% is the same thing as 0.05, because 0.05 represents "five one-hundredths" or "five things for every hundred things".

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Let\'s rewrite your code a little bit (and I\'ll clean up the formatting somewhat).

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money = 546.97\nfor i in range(10):\n    week = i * 4\n    money += 16\n    money += (0.05 * money)\n    print("On week {week} you have {money:.2f} dollars.".format(week=week, money=money))\n

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I made a few adjustments:

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• Instead of manually incrementing both i and week, let the loop take care of that;\xc2\xa0that\'s what it\'s for, after all!
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• Replaced (5% money) with (0.05 * money), which is how Python will understand what you want
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• Replaced your print statements with a single statement\n\n
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  • Used the advanced formatting {__:.2f} to produce a number that cuts off to just two decimal places (which is usual for money, but you can erase the :.2f if you want the full floating-point value)
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  • 有关这些参数如何工作的更多信息，请参阅6.1.3 \xe2\x80\x94\xc2\xa0Format String Syntax
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• 替换语句如money = money + xwithmoney += x because it\'s more concise and easier to read to advanced programmers (in my opinion)
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• 调整运算符周围的空白以提高可读性
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