[issue6871] decimal.py: more format issues

[Eric V. Smith]

Eric V. Smith  added the comment:

Thanks, Irit.

I'm closing this as "won't fix".

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resolution: out of date -> wont fix
stage:  -> resolved
status: open -> closed

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[issue6871] decimal.py: more format issues

[Irit Katriel]

Irit Katriel  added the comment:

No just trying to sort out the backlog.

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[issue6871] decimal.py: more format issues

[Eric V. Smith]

Eric V. Smith  added the comment:

I tend to agree with Mark: any change would be disruptive, and it doesn't seem 
to be causing any real problem.

Irit: did you come across this because it's causing a problem somewhere?

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[issue6871] decimal.py: more format issues

[Mark Dickinson]

Mark Dickinson  added the comment:

Eric: any thoughts on this?

It's looking like a "won't fix" to me. Regardless of what we think the "right" 
thing to do is, making the float behaviour stricter would be a backwards 
compatibility break, and relaxing the Decimal behaviour involves either 
diverging from the upstream libmpdec (and then having to maintain that 
divergence if we update to newer versions of libmpdec) or pushing changes back 
upstream. Both of those options seem like more effort than it's worth for 
something that apparently hasn't actually bothered anyone for several years.

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[issue6871] decimal.py: more format issues

[Irit Katriel]

Irit Katriel  added the comment:

Issue #2 still exists in 3.11:

>>> format(float(123), "00")
'123.0'
>>> format(Decimal(123), "00")
Traceback (most recent call last):
  File "", line 1, in 
ValueError: invalid format string

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versions: +Python 3.11

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[issue6871] decimal.py: more format issues

[Mark Lawrence]

Changes by Mark Lawrence breamore...@yahoo.co.uk:


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[issue6871] decimal.py: more format issues

[Mark Lawrence]

Mark Lawrence added the comment:

If I'm reading this correctly only issue 2 is outstanding.  Opinions please 
gentlemen.

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[issue6871] decimal.py: more format issues

[Eric Smith]

Eric Smith e...@trueblade.com added the comment:

I think there are no remaining issues here that don't have their own issue. I'm 
going to close this unless one of you think otherwise.

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assignee:  - eric.smith
resolution:  - out of date
status: open - pending
type:  - behavior

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[issue6871] decimal.py: more format issues

[Stefan Krah]

Stefan Krah stefan-use...@bytereef.org added the comment:

I couldn't find other issues where #1 and #2 are addressed. This
is from py3k:


#1:

 format(float('nan'), '+08.4')
'+nan'
[70141 refs]
 format(Decimal('nan'), '+08.4')
'+NaN'


#2: format(float(123), 00)
'123.0'
[70141 refs]
 format(Decimal(123), 00)
Traceback (most recent call last):
  File stdin, line 1, in module
  File /home/stefan/svn/py3k/Lib/decimal.py, line 3633, in __format__
spec = _parse_format_specifier(specifier, _localeconv=_localeconv)
  File /home/stefan/svn/py3k/Lib/decimal.py, line 5915, in 
_parse_format_specifier
raise ValueError(Invalid format specifier:  + format_spec)
ValueError: Invalid format specifier: 00
[70141 refs]

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[issue6871] decimal.py: more format issues

[Stefan Krah]

Stefan Krah stefan-use...@bytereef.org added the comment:

[The tracker apparently set the status to 'open' without my intervention.]

To sum up what I said earlier about #1 and #2, I think that the C standard
and gcc's warning behavior support the way of Decimal.

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[issue6871] decimal.py: more format issues

[Eric Smith]

Eric Smith e...@trueblade.com added the comment:

[If the status is pending, any comment turns it back to open, by design.]

I'd rather float.__format__ agree with %-formatting for floats than with 
anything else.

 '%+08.4f' % float('nan')
'+nan'
 %00f % float('123')
'123.00'

(Not sure about the precision being displayed on that last one, I'll have to 
think about it.)

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[issue6871] decimal.py: more format issues

[Mark Dickinson]

Mark Dickinson dicki...@gmail.com added the comment:

I think issue #4 is a bug in float formatting:  I don't think it makes 
sense to change alignment just because the fill character happens to be 
'0'.

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[issue6871] decimal.py: more format issues

[Mark Dickinson]

Mark Dickinson dicki...@gmail.com added the comment:

From the current trunk:

 format(float('1e88'), '120')
'1e+88111'
[64734 refs]
 format(float('1e88'), '020')
'0001e+88'
[64734 refs]

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[issue6871] decimal.py: more format issues

[Eric Smith]

Eric Smith e...@trueblade.com added the comment:

Created issue 6902 to handle #4.

The others will need to be broken out into their own issues if we want
to fix them. I can't keep track of multiple issues in one bug report.

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[issue6871] decimal.py: more format issues

[Stefan Krah]

Stefan Krah stefan-use...@bytereef.org added the comment:

Issue 3 is nonsense, '-' means left-justified in C. Sorry.

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[issue6871] decimal.py: more format issues

[Stefan Krah]

New submission from Stefan Krah stefan-use...@bytereef.org:

Hi,

I've two more issues where format behavior should probably be identical:

1: (version 2.6 vs. 3.1):

Version 2.6:
 format(Decimal(NaN), +08.4)
'+NaN'
 format(float(NaN), +08.4)
'+00.0nan'

Version 3.1:
 format(Decimal(NaN), +08.4)
'+NaN'
 format(float(NaN), +08.4)
'+nan'


2: (float vs. decimal):

 format(float(123), 00)
'123.0'
 format(Decimal(123), 00)
Traceback (most recent call last):
  File stdin, line 1, in module
  File /usr/lib/python3.1/decimal.py, line 3611, in __format__
spec = _parse_format_specifier(specifier, _localeconv=_localeconv)
  File /usr/lib/python3.1/decimal.py, line 5563, in
_parse_format_specifier
raise ValueError(Invalid format specifier:  + format_spec)
ValueError: Invalid format specifier: 00

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messages: 92453
nosy: marketdickinson, skrah
severity: normal
status: open
title: decimal.py: more format issues

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[issue6871] decimal.py: more format issues

[Eric Smith]

Eric Smith e...@trueblade.com added the comment:

For #1 for floats, 2.6 is in error. This has been fixed in 2.7 (trunk).

For #2, I think float is correct. The PEP says the specifier is:
[[fill]align][sign][#][0][minimumwidth][.precision][type]
so '00' is parsed as minimumwidth=0 with zero-padding specified.

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[issue6871] decimal.py: more format issues

[Eric Smith]

Eric Smith e...@trueblade.com added the comment:

Also, see issue 4482 for a discussion of float formatting for nan and inf.

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[issue6871] decimal.py: more format issues

[Mark Dickinson]

Mark Dickinson dicki...@gmail.com added the comment:

Issue #1: In both trunk and py3k I get:

 from decimal import Decimal
 format(Decimal('nan'), '+08.4')
'+NaN'
 format(float('nan'), '+08.4')
'+nan'
 format(Decimal('inf'), '+012.4')
'   +Infinity'
 format(float('inf'), '+012.4')
'+inf'

Two potential issues here:  first is the zero padding; to me, a zero-
padded nan or inf just looks ugly, but if people think that's the 
correct output (and I suppose that I have to admit that it probably is) 
then I'll add the zeros in for the Decimal type.

The second issue is the difference in spelling; ('nan' versus 'NaN', 
'inf' versus 'Infinity');  I'm not really bothered by this difference, 
and it would be quite awkward to change.  The output format for Decimal 
is mandated by the standard, while changing the spelling for floats 
seems both unnecessary and likely to break code.

Issue #2: This is a bit odd.  If a minimumwidth of 0 is permissible, 
then the format '0' is ambiguous.  Assuming that '0' continues to mean 
zero-padded, this leaves '00' as the *only* way to specify a minimum 
width of 0.  It seems cleaner just to assume that minimumwidth always 
has to be strictly positive, making '00' invalid.  At least, I think 
that's what I was thinking when I wrote the Decimal formatting code.
But I agree that float and Decimal should be consistent here.

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[issue6871] decimal.py: more format issues

[Stefan Krah]

Stefan Krah stefan-use...@bytereef.org added the comment:

Issue 1:

I would definitely keep the spelling in decimal, my concern was only the
padding.

The C standard agrees with Mark's view:

Leading zeros (following any indication of sign or base) are used to
pad to the field width rather than performing space padding, except when
converting an infinity or NaN.

If this could be agreed on, issue 1 should be handled by changing float
and decimal 2.6.


Issue 2:

I can't find it quickly in the C standard, but gcc warns in this situation:

   warning: repeated '0' flag in format

This would support the behavior of decimal and float should be changed.


I would like to add two new issues.

Issue 3:

Regarding padding, the C standard further says:

If the 0 and - flags both appear, the 0 flag is ignored

This is quite sensible, since signless 0 padding looks a bit awkward.
(But this is a minor issue). 


Issue 4:

 format(Decimal('1e88'), '020')
'1E+88000'

 format(float('1e88'), '020')
'0001e+88'

I think right-padding with digits is dangerous, since it changes the
numerical value. I'm not sure what float does, it doesn't look correct
(but protects the user).

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