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From: Terry Reedy <tjreedy@udel.edu>
Newsgroups: comp.lang.python
Subject: Re: Curious Omission In New-Style Formats
Date: Mon, 11 Jul 2016 16:52:00 -0400
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On 7/11/2016 3:27 PM, Ian Kelly wrote:
> On Mon, Jul 11, 2016 at 12:54 PM, Terry Reedy <tjreedy@udel.edu> wrote:
>> In any case, I think it an improvement to say that '0x00123' has a field
>> width of 7 rather than a 'precision' of 5.
>>
>>>>> '{:#07x}'.format(0x123)  # specifiy field width
>> '0x00123'
>>>>> "%#0.5x" % 0x123  # specify int precision
>> '0x00123'
>
> It occurs to me now that this does create a challenge if the format is
> meant to support negative numbers as well:
>
>>>> '%#0.5x' % -0x123
> '-0x00123'

This expands the field from 7 to 8 chars.  In running text, this is 
alright.  In formatted table columns, it is not.

>>>> '{:#07x}'.format(-0x123)
> '-0x0123'

Multiple alternatives

 >>> '{: #08x} {: #08x}'.format(0x123, -0x123)
' 0x00123 -0x00123'
 >>> '{:+#08x} {:+#08x}'.format(0x123, -0x123)
'+0x00123 -0x00123'
 >>> '{0:#0{1}x} {2:+#0{3}x}'.format(0x123, 7, -0x123, 8)
'0x00123 -0x00123'
 >>> n1, n2, w = 0x123, -0x123, 7
 >>> '{0:#0{1}x} {2:+#0{3}x}'.format(n1, w+(n1<0), n2, w+(n2<0))
'0x00123 -0x00123'

In running text, I ight go with '+','-' prefix.

-- 
Terry Jan Reedy