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, works with Decimal() against the doc of **Format Specification Mini-Language** #136636
Description
Bug report
Bug description:
The doc of Format Specification Mini-Language doesn't say that , works with Decimal() as shown below:
',': Inserts a comma every 3 digits for integer presentation type 'd' and floating-point presentation types, excluding 'n'. For other presentation types, this option is not supported.
But , works with Decimal() against the doc as shown below:
from decimal import Decimal
v = Decimal(value='1234.5555555555')
print('"{:,.20f}"'.format(v))
print('"{:,.20F}"'.format(v))
# "1,234.55555555550000000000"
# | 20 |
print('"{:,f}"'.format(v))
print('"{:,F}"'.format(v))
# "1,234.5555555555"
# | 10 |from decimal import Decimal
v = Decimal('123456.78912')
print('"{:,.20g}"'.format(v))
print('"{:,.20G}"'.format(v))
print('"{:,.20}"'.format(v))
print('"{:,g}"'.format(v))
print('"{:,G}"'.format(v))
print('"{:,}"'.format(v))
# "123,456.78912"
# | 11 |In addition, the doc doesn't say that _ works with Decimal() as shown below:
'_': Inserts an underscore every 3 digits for integer presentation type 'd' and floating-point presentation types, excluding 'n'. For integer presentation types 'b', 'o', 'x', and 'X', underscores are inserted every 4 digits. For other presentation types, this option is not supported.
So, _ doesn't work with Decimal() as the doc doesn't say so as shown below:
from decimal import Decimal
v = Decimal(value='1234.5555555555')
print('"{:_.20f}"'.format(v))
print('"{:_.20F}"'.format(v))
print('"{:_f}"'.format(v))
print('"{:_F}"'.format(v))
# ValueError: invalid format stringfrom decimal import Decimal
v = Decimal('123456.78912')
print('"{:_.20g}"'.format(v))
print('"{:_.20G}"'.format(v))
print('"{:_.20}"'.format(v))
print('"{:_g}"'.format(v))
print('"{:_G}"'.format(v))
print('"{:_}"'.format(v))
# ValueError: invalid format stringCPython versions tested on:
3.12
Operating systems tested on:
Windows
Activity
picnixz commentedon Jul 13, 2025
I'm not sure I understand the first issue namely with
,. The grammar says:So
,is supported as you observed (both for integer and floating-point presentations). As for_, do you mean that it doesn't work for any of the floating-point presentation types? I don't have access to a 3.13+ installation so I can't check. Also, in the future, please check the bugs against the stable versions, and not those that are security-only.cc @skirpichev
skirpichev commentedon Jul 14, 2025
This is certainly not a bug. The Decimal formatting is documented on the quoted page, as it says that available presentation types for floats and Decimals are same.
On the other hand, the Decimal is not a builtin type, maybe it's better to document it's formatting separately, as for Fractions, in the module page. (Right now it even has no examples of formatted output, see #128698.)
terryjreedy commentedon Jul 14, 2025
The "floating-point presentation types" are the implicit or explict f,F,g,G, not the object type. I don't see why you are getting the error messages. Maybe a fixed bug. In installed 3.14.0b4 and main:
Same with f-strings.
EDIT: Mismatches between presentation type and object type are ValueErrors.
skirpichev commentedon Jul 14, 2025
Ah, I thought my patch was backported: #132155
skirpichev commentedon Jul 14, 2025
Backport for 3.13: #136649
3.12 is security-only, so we can't do anything here.
StanFromIreland commentedon Jul 14, 2025
Backport has been merged, should this not be classified as a duplicate of its issue?
picnixz commentedon Jul 14, 2025
Yes, it would be a duplicate now.