BUG: fix precision to specify decimal places

[drewrey]

• closes Pandas style.set_precision not working as expected #13257
• tests added / passed
• passes git diff upstream/master | flake8 --diff
• whatsnew entry

Use 'f' as a string conversion type to specify the number of decimals to
represent. The 'g' format will instead fall back to the 'e' format
causing the unexpected behavior seen in GHI13257.

See: old-string-formatting

Replicated code from the issue, with output:

[sinhrks]

pls also test changing the precision from default.

[sinhrks]

Also, add tests with Float64Index like:

df = pd.DataFrame(data = np.random.randn(4,4),
                  index=[11.1, 22.2, 33.3, 44.4]
                  columns=[1.1111, 2.2222, 3.3333, 4.4444])

[codecov-io]

Current coverage is 85.28% (diff: 100%)

Merging #13897 into master will decrease coverage by <.01%

@@             master     #13897   diff @@
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  Methods           0          0          
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- Hits          42692      42691     -1   
- Misses         7365       7366     +1   
  Partials          0          0          

Powered by Codecov. Last update 45d54d0...0731bcb

[jreback]

@TomAugspurger ?

@drewrey pls add a whatsnew note (bug fix section)

[TomAugspurger]

Changing it to g was intentional to avoid things like

In [1]: "{:f}".format(1)
Out[1]: '1.000000'

and instead have that formatted as 1. I glanced quickly and didn't see any tests for that :/

Could you add a test with an integer and a float column like 1.0, use the default precision / formatter, and verify that the display value is 1, and then make sure your change passes that test?

[TomAugspurger]

Looking further, it seems like we have a bug in master.

m = pd.DataFrame({"a": [1], "b": [1.]})

m.style._translate()['body'][0][1]['display_value'] # should be '1', is correct

m.style._translate()['body'][0][2]['display_value'] # should be '1.0', currently is '1', is incorrect

Ideally df.style would have the same output as df._repr_html() by default.

[jreback]

can you rebase / update?

[jreback]

can you add a whatnew note in 0.19.2

@TomAugspurger ?

[jreback]

closing, but if you'd like to update, pls do so.