Format string - spaces between every three digit

Question

How to simple format string with decimal number for show it with spaces between every three digits?

I can make something like this:

some_result = '12345678,46'
' '.join(re.findall('...?', test[:test.find(',')]))+test[test.find(','):]

and result is:

'123 456 78,46'

but I want:

'12 345 678,46'

Answer 1

This is a bit hacky, but:

format(12345678.46, ',').replace(',', ' ').replace('.', ',')

As described in Format specification mini-language, in a format_spec:

The ',' option signals the use of a comma for a thousands separator.

Then we just replace each comma with a space, then the decimal point with a comma, and we're done.

For more complex cases using str.format instead of format, the format_spec goes after the colon, as in:

'{:,}'.format(12345678.46)

See PEP 378 for details.

---

Meanwhile, if you're just trying to use the standard grouping and separators for your system's locale, there are easier ways to do that—the n format type, or the locale.format function, etc. For example:

>>> locale.setlocale(locale.LC_NUMERIC, 'pl_PL')
>>> format(12345678, 'n')
12 345 678
>>> locale.format('%.2f' 12345678.12, grouping=True)
12 345 678,46
>>> locale.setlocale(locale.LC_NUMERIC, 'fr_FR')
>>> locale.format('%.2f' 12345678.12, grouping=True)
12345678,46
>>> locale.setlocale(locale.LC_ALL, 'en_AU')
>>> locale.format('%.2f' 12345678.12, grouping=True)
12,345,678.46

If your system locale is, say, pl_PL, just calling locale.setlocale(locale.LC_NUMERIC) (or locale.setlocale(locale.LC_ALL)) will pick up the Polish settings that you want, but the same person running your program in Australia will pick up the Australian settings that he wants.

Answer 2

I think a regex would be much nicer:

>>> import re
>>> some_result = '12345678,46'
>>> re.sub(r"\B(?=(?:\d{3})+,)", " ", some_result)
'12 345 678,46'

Explanation:

\B       # Assert that we're not at the start of a number
(?=      # Assert that the following regex could match from here:
 (?:     # The following non-capturing group
  \d{3}  # which contains three digits
 )+      # and can be matched one or more times
 ,       # until a comma follows.
)        # End of lookahead assertion

Answer 3

Use:

' '.join(re.findall('...?',test[:test.find(',')][::-1]))[::-1]+test[test.find(','):]

You have used regex which starts matching a string from the start. But you want to group the 3 numbers from the end (before comma).

So reverse the string before comma, apply the same logic and then reverse it back.