CLN: Old string formatting: .format() -> f

[DorAmram]

• ref Replace old string formatting syntax with f-strings #29547
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[pep8speaks]

Hello @DorAmram! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-12-22 18:03:07 UTC

[topper-123]

Looks good, a single issue.

[topper-123]

don't use triple-quoted strings, it's not the same as two single-quoted strings.

[alimcmaster1]

Hmm I think this file is autogenerated as per @jbrockmendel comments here #29518 (comment)

[jreback]

yeah we can leave this one alone, do we have a check for .format usage in checks? (prob not yet)

[alimcmaster1]

yeah we can leave this one alone, do we have a check for .format usage in checks? (prob not yet)

Not yet there are still 200+ files to tackle.
grep -l -R -e '%s' -e '%d' -e '\.format(' --include=*.{py,pyx} pandas/

If we want to add a check now we can do - and users remove the file from exclude list once done?
(Would help confirm all instances of .format have been removed in the PR for a file)

[jbrockmendel]

grepping for .format( will be complicated by the fact that we have 6 places where we def format\(. But we can worry about that later. This PR is non-actionable, closing.