python - Convert decimal mark when reading numbers as input

Question

I have a CSV file with data reading that I want to read into Python. I get lists that contain strings like "2,5". Now doing float("2,5") does not work, because it has the wrong decimal mark.

How do I read this into Python as 2.5?

Answer 1

您可以使用区域感知方式进行操作：

import locale

# Set to users preferred locale:
locale.setlocale(locale.LC_ALL, '')
# Or a specific locale:
locale.setlocale(locale.LC_NUMERIC, "en_DK.UTF-8")

print locale.atof("3,14")

使用此方法前请阅读本节。

Answer 2

float("2,5".replace(',', '.'))在大多数情况下都可以

如果value是一个很大的数字并且.已经使用了数千个，您可以：

将所有逗号替换为点：value.replace(",", ".")

删除除最后一点之外的所有内容：value.replace(".", "", value.count(".") -1)

Answer 3

Pandas supports this out of the box:

df = pd.read_csv(r'data.csv', decimal=',')

See http://pandas.pydata.org/pandas-docs/stable/generated/pandas.read_csv.html

Answer 4

using a regex will be more reliable

import re

decmark_reg = re.compile('(?<=\d),(?=\d)')

ss = 'abc , 2,5 def ,5,88 or (2,5, 8,12, 8945,3 )'

print ss
print decmark_reg.sub('.',ss)

result

abc , 2,5 def ,5,88 or (2,5, 8,12, 8945,3 )
abc , 2.5 def ,5.88 or (2.5, 8.12, 8945.3 )

If you want to treat more complex cases (numbers with no digit before the decimal mark for exemple) the regex I crafted to detect all types of numbers in the following thread may be of interest for you:

stackoverflow.com/questions/5917082/regular-expression-to-match-numbers-with-or-without-commas-and-decimals-in-text/5929469

Answer 5

首先，您必须确保用于提供号码的区域设置。不这样做肯定会发生随机问题。

import locale

loc = locale.getlocale()  # get and save current locale
# use locale that provided the number;
# example if German locale was used:
locale.setlocale(locale.LC_ALL, 'de_DE')
pythonnumber = locale.atof(value)
locale.setlocale(locale.LC_ALL, loc)  # restore saved locale

Answer 6

尝试用小数点替换所有小数点逗号：

floatAsStr = "2,5"
floatAsStr = floatAsStr.replace(",", ".");
myFloat = float(floatAsStr)

当然，该函数replace适用于任何子字符串，因为 python 现在确实区分了 char 和 string。

Answer 7

如果将点用作千位分隔符，要交换逗号和点，您可以使用第三个符号作为临时占位符，如下所示：

value.replace('.', '#').replace(',', '.').replace('#', ',')

但是看到你想从字符串转换为浮点数，你可以删除任何点，然后用点替换任何逗号

float(value.replace('.', '').replace(',', '.'))

IMO这是最易读的解决方案