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

18,660

Solution 1

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'

Solution 2

As @michel-de-ruiter mentioned, the f format does not work with locale. On the other hand, you can't set the precision using n format. For example, if you want 4 digits after decimal separator:

import locale
locale.setlocale(locale.LC_ALL, 'nl_NL')

position = 123.45678999
print(f'{position:.4n}')  # output: 123,4 (not quite what we wanted!)

However, you can round the number with the desired precision before formatting it:

print(f'{round(position, 4):n}')  # output: 123,4567 (that's it!)

Solution 3

If the g format is good enough for you, use n instead:

resultfile.write(f"Position\t{position:.7n}")

While n works (uses the current locale setting when used) instead of both d and g, there is no such thing for the f format unfortunately...

Share:
18,660

Related videos on Youtube

seaver
Author by

seaver

engineer who likes math

Updated on June 04, 2022

Comments

  • seaver
    seaver over 1 year

    For some machine control in python, I write the results to a text-file, that someone else can copy into Excel (this is the most convenient way in this situation). However, in the Netherlands, Excel has a comma as decimal separator and thus I want to have the result "position" in the text-file as 123,456, but when I use the f-string method like this:

        resultfile.write(f"Position\t{position:.5}")
    

    This will obviously result in a dot decimal separator.

    How can I change this to a comma without iterating through the whole file int the end and replace the dots with commas?

    • Arne
      Arne over 4 years
      An fstring is just a string, so f"Position\t{position:.5}".replace('.', ',') should work just fine, right?
    • Arne
      Arne over 4 years
      Also: stackoverflow.com/a/6633912/962190 This answer talks about a different issue (printing number with comma separation every three decimal positions), but the locale setting might influence your format as well.
  • marcelm
    marcelm about 3 years
    This changes the thousands separator to , but the question is asking about the decimal separator. It doesn't answer the question at all.
  • Michel de Ruiter
    Michel de Ruiter almost 3 years
    @seaver This does not answer the question. All this does is introducing a thousands separator (,). It does not change the decimal separator (stays .).