158 – Grouping digits in the fractional part

You can group digits in integers with underscores or commas, but since Python 3.14 that you can also do the same to the digits of the fractional part of a number.

x = 12345.09876543

f"{x:.,}"  # '12345.098,765,43'
f"{x:._}"  # '12345.098_765_43'

The grouping can be specified independently for the digits before and after the decimal point by including a grouping character before or after the dot in the formatting specification:

f"{x:_.,}"  # '12_345.098,765,43'

Remember that if you only specify the grouping character, it will only group the digits of the integral part (see “Formatting big numbers”):

f"{x:_}"  # '12_345.09876543'