On 1/29/2018 2:13 AM, Nick Coghlan wrote:
On 29 January 2018 at 11:48, Nathaniel Smith <n...@pobox.com> wrote:
On Sun, Jan 28, 2018 at 5:31 PM, David Mertz <me...@gnosis.cx> wrote:
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:
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}")
This just seems too complicated to me, and is overgeneralizing. How many
of these different formats would ever really be used? Can you really
expect someone to remember what that means by looking at it?
If you are going to generalize it, at least go all the way and support
the struct lconv "CHAR_MAX" behavior, too.
However, I suggest just pick another character to use instead of ",",
and have it mean the 2,3 format. With no evidence (and willing to be
wrong), it seems like it's the next-most needed variety of this. Maybe
use ";"?
Eric
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.
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