在 Python 2.7 中四舍五入到两位小数？
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Rounding to two decimal places in Python 2.7?
提问by RCN
Using Python 2.7 how do I round my numbers to two decimal places rather than the 10 or so it gives?
使用 Python 2.7 如何将我的数字四舍五入到两位小数而不是它给出的 10 左右？
print "financial return of outcome 1 =","$"+str(out1)
回答by Ashwini Chaudhary
Use the built-in function round():
使用内置函数round()：
>>> round(1.2345,2)
1.23
>>> round(1.5145,2)
1.51
>>> round(1.679,2)
1.68
Or built-in function format():
或内置函数format()：
>>> format(1.2345, '.2f')
'1.23'
>>> format(1.679, '.2f')
'1.68'
Or new style string formatting:
或新样式字符串格式：
>>> "{:.2f}".format(1.2345)
'1.23
>>> "{:.2f}".format(1.679)
'1.68'
Or old style string formatting:
或旧式字符串格式：
>>> "%.2f" % (1.679)
'1.68'
help on round:
帮助round：
>>> print round.__doc__
round(number[, ndigits]) -> floating point number
Round a number to a given precision in decimal digits (default 0 digits).
This always returns a floating point number. Precision may be negative.
回答by John Doe
print "financial return of outcome 1 = $%.2f" % (out1)
回答by TerryA
You can use str.format(), too:
您也可以使用str.format()：
>>> print "financial return of outcome 1 = {:.2f}".format(1.23456)
financial return of outcome 1 = 1.23
回答by teewuane
When working with pennies/integers. You will run into a problem with 115 (as in $1.15) and other numbers.
使用便士/整数时。您将遇到 115（如 1.15 美元）和其他数字的问题。
I had a function that would convert an Integer to a Float.
我有一个函数可以将整数转换为浮点数。
...
return float(115 * 0.01)
That worked most of the time but sometimes it would return something like 1.1500000000000001.
这在大多数情况下都有效，但有时它会返回类似1.1500000000000001.
So I changed my function to return like this...
所以我改变了我的函数来像这样返回......
...
return float(format(115 * 0.01, '.2f'))
and that will return 1.15. Not '1.15'or 1.1500000000000001(returns a float, not a string)
这将返回1.15。Not '1.15'or 1.1500000000000001（返回一个浮点数，而不是一个字符串）
I'm mostly posting this so I can remember what I did in this scenario since this is the first result in google.
我主要是发布这个，所以我可以记住我在这个场景中做了什么，因为这是谷歌的第一个结果。
回答by Ronan Paix?o
Since you're talking about financialfigures, you DO NOT WANTto use floating-point arithmetic. You're better off using Decimal.
既然你在谈论金融数据，你不希望使用浮点运算。最好使用十进制。
>>> from decimal import Decimal
>>> Decimal("33.505")
Decimal('33.505')
Text output formatting with new-style format()(defaults to half-even rounding):
使用新样式的文本输出格式format()（默认为半偶数舍入）：
>>> print("financial return of outcome 1 = {:.2f}".format(Decimal("33.505")))
financial return of outcome 1 = 33.50
>>> print("financial return of outcome 1 = {:.2f}".format(Decimal("33.515")))
financial return of outcome 1 = 33.52
See the differences in rounding due to floating-point imprecision:
请参阅由于浮点不精确而导致的舍入差异：
>>> round(33.505, 2)
33.51
>>> round(Decimal("33.505"), 2) # This converts back to float (wrong)
33.51
>>> Decimal(33.505) # Don't init Decimal from floating-point
Decimal('33.50500000000000255795384873636066913604736328125')
Proper way to round financial values:
四舍五入财务价值的正确方法：
>>> Decimal("33.505").quantize(Decimal("0.01")) # Half-even rounding by default
Decimal('33.50')
It is also common to have other types of rounding in different transactions:
在不同的交易中使用其他类型的舍入也很常见：
>>> import decimal
>>> Decimal("33.505").quantize(Decimal("0.01"), decimal.ROUND_HALF_DOWN)
Decimal('33.50')
>>> Decimal("33.505").quantize(Decimal("0.01"), decimal.ROUND_HALF_UP)
Decimal('33.51')
Remember that if you're simulating return outcome, you possibly will have to round at each interest period, since you can't pay/receive cent fractions, nor receive interest over cent fractions. For simulations it's pretty common to just use floating-point due to inherent uncertainties, but if doing so, always remember that the error is there. As such, even fixed-interest investments might differ a bit in returns because of this.
请记住，如果您正在模拟回报结果，您可能必须在每个利息期进行四舍五入，因为您无法支付/接收美分分数，也无法获得超过美分分数的利息。对于模拟，由于固有的不确定性，通常只使用浮点数，但如果这样做，请始终记住错误就在那里。因此，即使是固定利息投资的回报也可能因此而有所不同。
回答by Thiago Santos
The best, I think, is to use the format()function:
我认为最好的方法是使用format()函数：
>>> print("financial return of outcome 1 = $ " + format(str(out1), '.2f'))
// Should print: financial return of outcome 1 = $ 752.60
But I have to say: don't use round or format when working with financial values.
但我不得不说：在处理财务价值时不要使用圆形或格式。
回答by Shan Niz
A rather simple workaround is to convert the float into string first, the select the substring of the first four numbers, finally convert the substring back to float. For example:
一个相当简单的解决方法是先将浮点数转换为字符串，然后选择前四个数字的子字符串，最后将子字符串转换回浮点数。例如：
>>> out1 = 1.2345
>>> out1 = float(str(out1)[0:4])
>>> out1
May not be super efficient but simple and works :)
可能不是超级高效但简单有效:)
回答by Midhun M M
When we use the round() function, it will not give correct values.
当我们使用 round() 函数时，它不会给出正确的值。
you can check it using, round (2.735) and round(2.725)
您可以使用 round (2.735) 和 round(2.725) 检查它
please use
请用
import math
num = input('Enter a number')
print(math.ceil(num*100)/100)
回答by Lucas VL
Rounding up to the next 0.05, I would do this way:
四舍五入到下一个 0.05，我会这样做：
def roundup(x):
return round(int(math.ceil(x / 0.05)) * 0.05,2)
