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?

Asked By: Jan

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Source

Answer 1

You can’t have more than one dot (.) or comma (,) in your number since both of these symbols are used by atof() to separate the decimal part of your number from its integer part.

Since the dots are not needed for Python to correctly represent your number, you should remove them and only keep the comma:

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

string_nb = '17.907,08'
string_nb = string_nb.replace('.', '')
number = atof(string)

Answered By: Ronan Boiteau

Answer 2

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

Answered By: Jan

Answer 3

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

Answered By: Panagiotis Kanavos

Convert a number using atof

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