Convert a number using atof

Question

In Python 3.5, I'd like to convert a German number string to a float using locale.atof with the following code:

---

import locale
from locale import atof
locale.setlocale(locale.LC_ALL, 'de_DE')

number = atof('17.907,08')

However, this raises a ValueError:

ValueError: could not convert string to float: '17.907.08'

---

Why? Isn't this exactly what atof() was made for?

Answer 1

Just for future reference - this is what I ended up using:

import locale
from locale import atof

def convert(string, thousands_delim = '.', abbr = 'de_DE.UTF-8'):
    ''' Converts a string to float '''

    locale.setlocale(locale.LC_ALL, abbr)
    try:
        number = atof("".join(string.split(thousands_delim)))
    except ValueError:
        number = None

    return number

---

You call it like

number = convert('17.907,08')
print(number)
# 17907.08

... or for English numbers:

number = convert('1,000,000', abbr = 'en_US')
print(number)
# 1000000.0

Answer 2

In Python 3.10 the works as expected

>>> from locale import atof
>>> import locale
>>> locale.setlocale( locale.LC_ALL, 'de_DE' )
'de_DE'
>>> atof('17.907,08')
17907.08

Using string manipulations to parse decimals is very fragile and should be avoided when possible. Using the wrong replacement could convert decimals to thousands and vice versa