[issue38657] String format for hexadecimal notation breaks padding with alternative form

[Pete Wicken]

Change by Pete Wicken :


--
keywords: +patch
pull_requests: +16548
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/17036

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue38657] String format for hexadecimal notation breaks padding with alternative form

[Vedran Čačić]

Vedran Čačić  added the comment:

It seems that you're confusing two things that really don't have much in common.

* (field) width is a _number_, saying how many characters (at least) should the 
formatted output take.
* padding is a bool (or maybe a char), saying what should be put inside the 
leftover space if the default formatted output is shorter than the width

The padding is not the width, and the width is not the padding. Once you start 
to differentiate those two things, I'm convinced all your confusions will 
disappear.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue38657] String format for hexadecimal notation breaks padding with alternative form

[Pete Wicken]

Pete Wicken  added the comment:

Given the comments above I appreciate that this is actually due to the padding 
being the total field width rather than the padding of the digits themselves. 
Having revised the documentation again, I believe this following line is 
explaining it:

"When no explicit alignment is given, preceding the width field by a zero ('0') 
character enables sign-aware zero-padding for numeric types. This is equivalent 
to a fill character of '0' with an alignment type of '='."

(https://docs.python.org/3.8/library/string.html)

I initially read "sign-aware zero-padding for numeric types" to mean the 
padding would not blindly prepend, and would take into account any signs and 
pad after (hence initially making this a bug). So maybe as suggested above we 
should explicitly mention the padding is the total number of characters in the 
field, rather than just the numbers.

I can look into adding this soon and see what you all think.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue38657] String format for hexadecimal notation breaks padding with alternative form

[Vedran Čačić]

Vedran Čačić  added the comment:

The width doesn't mean "the number of bits", it means "the width of the field". 
In every other case too:

* when we format negative numbers, width includes the minus sign
* when we format decimal numbers, width includes decimal point (or comma)
* when we format strings with !r, width includes the quotes

So, not only would it break too much code, but it would actually be 
inconsistent to formatting all other types currently.

--
nosy: +veky

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue38657] String format for hexadecimal notation breaks padding with alternative form

[Mark Dickinson]

Change by Mark Dickinson :


--
nosy: +mark.dickinson

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue38657] String format for hexadecimal notation breaks padding with alternative form

[Eric V. Smith]

Eric V. Smith  added the comment:

Now that I re-read this, maybe it was a documentation request, not a functional 
change? I'd be okay with documenting the existing behavior, so I'll re-open 
this and change the type. Patches welcome.

--
components: +Documentation
resolution: rejected -> 
stage: resolved -> needs patch
status: closed -> open
versions: +Python 3.9

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue38657] String format for hexadecimal notation breaks padding with alternative form

[Eric V. Smith]

Eric V. Smith  added the comment:

int.__format__ inherits this from %-formatting, which inherits it from C's 
printf.

There's no way we're going to change this at this point: the breakage would be 
too great. So, I'm going to reject this.

--
assignee:  -> eric.smith
nosy: +eric.smith
resolution:  -> rejected
stage:  -> resolved
status: open -> closed

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue38657] String format for hexadecimal notation breaks padding with alternative form

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Yes, the width is the width of the formatted value, not the number of digits.

What is your proposition?

--
nosy: +serhiy.storchaka

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue38657] String format for hexadecimal notation breaks padding with alternative form

[Pete Wicken]

New submission from Pete Wicken :

When formatting an integer as a hexadecimal value, the '#' alternate form 
modifier inserts a preceding '0x'. 
If this is used in combination with padding modifiers, the '0x' is counted as 
part of the overall width, which does not feel like the natural behaviour as 
extra calculation is required to get the correct post '0x' precision.

Example:

In [7]: f'{num:04x}'
Out[7]: '0800'

In [8]: f'{num:#04x}'
Out[8]: '0x800'

To get the hexadecimal representation padded to 4 digits, you have to account 
for the preceding 0x:

In [10]: f'{num:#06x}'
Out[10]: '0x0800'

--
messages: 355767
nosy: Wicken
priority: normal
severity: normal
status: open
title: String format for hexadecimal notation breaks padding with alternative 
form
type: behavior
versions: Python 3.7, Python 3.8

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com