Re: [Python-ideas] Format mini-language for lakh and crore

Nick suggests: >>> print(f"In European format x is {x:,.2f}, in Indian format it is {x:,2,3.2f}") This looks very good and general. I only know of the "European" and South Asian conventions in widespread use, but we could give other grouping conventions using that little syntax and it definitely covers the ones I know about. There's not an issue about this giving the parser for the format mini-language hiccups over width specifier in there, is there? On Mon, Jan 29, 2018 at 2:13 AM, Nick Coghlan wrote:

On 29 January 2018 at 11:48, Nathaniel Smith wrote:

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On Sun, Jan 28, 2018 at 5:31 PM, David Mertz wrote:

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I actually didn't know about `locale.format("%d", 10e9, grouping=True)`. But it's still much less general than having the option in the f-string/.format() mini-language. This is really about the formatted string, not necessarily about the locale. So, e.g. I'd like to be able to write:

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print(f"In European format x is {x:,.2f}, in Indian format it is {x:`.2f}")

I don't want the format necessarily to be some pseudo-global setting, even if it can get stored in thread-locals. That said, having a locale-aware symbol for delimiting numbers in the format mini-language would also not be a bad thing.

I don't understand the format mini-language well enough to know what would fit in, but maybe some way to (a) request localified formatting,

Given the example, I think a more useful approach would be to allow an optional digit grouping specifier after the comma separator, and allow the separator to be repeated to indicate non-uniform groupings in the lower order digits.

If we did that, then David's example could become:

>>> print(f"In European format x is {x:,.2f}, in Indian format it is {x:,2,3.2f}")

The core elements of interpreting that would then be:

- digit group size specifiers are permited for both "," (decimal display only) and "_" (all display bases) - if no digit group size specifier is given, it defaults to 3 for decimal and 4 for binary, octal, and hexadecimal - if multiple digit group specifiers are given, then the last one given is applied starting from the least significant integer digit

so "{x:,2,3.2f}" means:

- an arbitrary number of leading 2-digit groups - 1 group of 3 digits - 2 decimal places

It would then be reasonably straightforward to use this as a lower level primitive to implement locale dependent formatting, as follows:

- format in English using the locale's grouping rules [1] (either LC_NUMERIC.grouping or LC_MONETARY.mon_grouping, as appropriate) - use str.translate() [2] to replace "," and "." with the locale's thousands_sep & decimal_point or mon_thousands_sep & mon_decimal_point

[1] https://docs.python.org/3/library/locale.html#locale.localeconv [2] https://docs.python.org/3/library/stdtypes.html#str.translate

Cheers, Nick.

-- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia

-- Keeping medicines from the bloodstreams of the sick; food from the bellies of the hungry; books from the hands of the uneducated; technology from the underdeveloped; and putting advocates of freedom in prisons. Intellectual property is to the 21st century what the slave trade was to the 16th.