In str.format "{0:#.5g}" for decimal.Decimal doesn't print trailing zeros

[py-user]

BPO	13838
Nosy	@mdickinson, @ericvsmith, @skrah, @py-user
Superseder	bpo-7094: Add alternate float formatting styles to new-style formatting.

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2012-01-23.15:18:19.886>
created_at = <Date 2012-01-22.22:25:29.728>
labels = ['interpreter-core', 'type-bug', 'library']
title = 'In str.format "{0:#.5g}" for decimal.Decimal doesn\'t print trailing zeros'
updated_at = <Date 2012-01-23.15:18:19.885>
user = 'https://github.com/py-user'

bugs.python.org fields:

activity = <Date 2012-01-23.15:18:19.885>
actor = 'eric.smith'
assignee = 'none'
closed = True
closed_date = <Date 2012-01-23.15:18:19.886>
closer = 'eric.smith'
components = ['Interpreter Core', 'Library (Lib)']
creation = <Date 2012-01-22.22:25:29.728>
creator = 'py.user'
dependencies = []
files = []
hgrepos = []
issue_num = 13838
keywords = []
message_count = 5.0
messages = ['151790', '151791', '151793', '151803', '151804']
nosy_count = 4.0
nosy_names = ['mark.dickinson', 'eric.smith', 'skrah', 'py.user']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = None
status = 'closed'
superseder = '7094'
type = 'behavior'
url = 'https://bugs.python.org/issue13838'
versions = ['Python 3.2']

[py-user]

http://docs.python.org/py3k/library/string.html#format-specification-mini-language

The '#' option:
"For floats, complex and Decimal the alternate form causes the result of the conversion to always contain a decimal-point character, even if no digits follow it. Normally, a decimal-point character appears in the result of these conversions only if a digit follows it. In addition, for 'g' and 'G' conversions, trailing zeros are not removed from the result."

1)
>>> import decimal
>>> '{0:#.5g}'.format(1.5)
'1.5000'
>>> '{0:.5f}'.format(decimal.Decimal(1.5))
'1.50000'
>>> '{0:.5g}'.format(decimal.Decimal(1.5))
'1.5'
>>> '{0:#.5g}'.format(decimal.Decimal(1.5))
'1.5'
>>>

no zeros with "#"

2)
>>> import decimal
>>> '{0:#.5g}'.format(decimal.Decimal('1.500000000000'))
'1.5000'
>>> '{0:.5g}'.format(decimal.Decimal('1.500000000000'))
'1.5000'
>>>

zeros without "#"

[ericvsmith]

See issue bpo-7098 for a discussion.

I propose to close this issue.

[py-user]

my question is about the "#" option
it is described as working with Decimal but it doesn't work with Decimal

[mdickinson]

IMO, the behaviour is fine; it's the docs that are unclear. The rules for Decimal are different mainly because trailing zeros have meaning for the Decimal type. (Decimal('1.250') and Decimal('1.25') are two distinct Decimal objects, unlike float('1.250') and float('1.25').)

See also issue bpo-7094.

[mdickinson]

Ah no, I take it back. I think (2) is fine---this is the usual preservation of trailing zeros where possible. (1) needs to be fixed (and issue bpo-7094 was left open waiting for this fix).