How to Convert a String with Dot and Comma into a Float in Python

How can I convert a string with dot and comma into a float in Python

Just remove the , with replace():

float("123,456.908".replace(',',''))

Convert Python strings into floats explicitly using the comma or the point as separators

because I don't know the locale settings

You could look that up using the locale module:

>>> locale.nl_langinfo(locale.RADIXCHAR)
'.'

or

>>> locale.localeconv()['decimal_point']
'.'

Using that, your code could become:

import locale
_locale_radix = locale.localeconv()['decimal_point']

def read_float_with_comma(num):
    if _locale_radix != '.':
        num = num.replace(_locale_radix, ".")
    return float(num)

Better still, the same module has a conversion function for you, called atof():

import locale

def read_float_with_comma(num):
    return locale.atof(num)

Convert number strings with commas in pandas DataFrame to float

If you're reading in from csv then you can use the thousands arg:

df.read_csv('foo.tsv', sep='\t', thousands=',')

This method is likely to be more efficient than performing the operation as a separate step.

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You need to set the locale first:

In [ 9]: import locale

In [10]: from locale import atof

In [11]: locale.setlocale(locale.LC_NUMERIC, '')
Out[11]: 'en_GB.UTF-8'

In [12]: df.applymap(atof)
Out[12]:
      0        1
0  1200  4200.00
1  7000    -0.03
2     5     0.00

How to format a float with a comma as decimal separator in an f-string?

If you want to format floats with a comma within the f-string, you can either use replace after casting the float to a string:

position = 123.456
f"Position\t{str(position).replace('.',',')}"

A second option is to use the Python standard library module locale (but it is not thread-safe):

import locale
locale.setlocale(locale.LC_ALL, 'nl_NL')
f"Position\t{locale.format('%.3f', position)}"

A third option is to use the library babel (preferred in case of library routines):

from babel.numbers import format_decimal
f"Position\t{format_decimal(position, locale='nl_NL')}"

All three options return the same result for the given example:

'Position\t123,456'

replace dot and comma with each other from a number str in python

You might want to rely on switching the locale of the number, should such an API exist within Python. If you must do the substitution manually, then use re.sub with lambda callback:

amt = '1.233.456.778,00'
output = re.sub(r'[.,]', lambda x: '.' if x.group() == ',' else ',', amt)
print(output)  # 1,233,456,778.00

Note that this approach gets around the problem with your current approach, namely that if the string happens to have an @ in it, then your logic would fail.

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