convert decimal mark

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

float("2,5".replace(',', '.')) will do in most cases

If valueis a large number and .has been used for thousands, you can:

Replace all commas for points: value.replace(",", ".")

Remove all but the last point: value.replace(".", "", value.count(".") -1)

Answer 2

You may do it the locale-aware way:

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")

Read this section before using this method.

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

Try replacing all the decimal commas with decimal dots:

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

The function replace, of course, work on any substring as python does now differentiate between char and string.

Answer 6

First you must ensure what locale was used to provide the number. Failing to do this random problems surely will occur.

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