It is recommended to use an em-dash instead of a hyphen for numerical ranges. It looks better in the rendered document. Python documentation already use it, but not always. Proposed patch adds more en-dashes.

While you are at it, have you checked how many en-dashes have been used instead of em-dashes?  "--" is commonly used to indicate em-dashes (e.g. in emails), but in rst it renders to an en-dash.

353 en-dashes with spaces.
479 em-dashes with spaces.
89 em-dashes without spaces.

And some number of hyphens with spaces. It is hard to automatically distinguish them from minuses in code examples, but in issue18529 I provided large patches that converted all of them to dashes.

Some of these double hyphens are in code examples. Thus the actual number of en-dashes that can be changed to em-dashes is smaller.

Personally I prefer en dashes where practical, but I fear the change may conflict with other people’s styles and preferences. I quickly counted 22 single hyphens (obviously I missed a few that your patch caught) and also 22 existing en dashes.

The rest single hyphens between digits are meaningful hypens in iso-8859-1, ISDNs, sample outputs, etc.

Sure, I was just saying that for whatever reason, 50% of the documentation uses hyphens for number ranges, and 50% uses en dashes.

> It is recommended to use an em-dash instead of a hyphen for numerical ranges.

Who makes that recommendation? Did you mean en-dash rather than em-dash?

> Did you mean en-dash rather than em-dash?

Ah, judging by the title and the patch, you did. :-) Phew!

Now I can delete the long post I had citing multiple sources for using en-dashes (not em-dashes) for numeric ranges...

My Australian Style Manual says to use en rules for spans of figures etc. Wikipedia mentions some other guides: <https://en.wikipedia.org/wiki/Dash#Ranges_of_values>; apparently some prefer the hyphen. That is why I said it is a style issue, not a black and white thing.

Sorry, yes, I meant en-dashes of course. I read this recommendation in many books about TeX, and also in other typographic resources. In modern fonts a hyphen-minus (U+002D) is shorter than digits in modern fonts and is placed lower than the middle of digits. An en-dash (U+2013) has the same width as digits and is placed higher, at the middle of digit's height.

> I read this recommendation in many books about TeX, and also in other typographic resources.

Same here. I'd add Apple's Style Guide and the Chicago Manual of Style to that list.

I checked the patch with Rietveld and all the changes are '-' to '--' in numeric ranges in text. LGTM.

New changeset 77307437ae15 by Serhiy Storchaka in branch '3.5':
Issue #28763: Use double hyphens (rendered as en-dashes) in numerical ranges
https://hg.python.org/cpython/rev/77307437ae15

New changeset 59bd48afa1bc by Serhiy Storchaka in branch '2.7':
Issue #28763: Use double hyphens (rendered as en-dashes) in numerical ranges
https://hg.python.org/cpython/rev/59bd48afa1bc

New changeset 3434d84efdd4 by Serhiy Storchaka in branch '3.6':
Issue #28763: Use double hyphens (rendered as en-dashes) in numerical ranges
https://hg.python.org/cpython/rev/3434d84efdd4

New changeset dc407f50e823 by Serhiy Storchaka in branch 'default':
Issue #28763: Use double hyphens (rendered as en-dashes) in numerical ranges
https://hg.python.org/cpython/rev/dc407f50e823

Thanks Terry.