Fix DataFrame.to_string() justification (2)

[gshiba]

• closes to_string formatters not as expected when header=False #16839,
  closes Justification is broken with to_string(index=False)  #13032
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

'Competes' with #22437 which attempts to revert % d to %d as suggested here: #13032 (comment) That turned out to affect a lot of tests, which in hindsight is expected; the % d has been around since at least 2012 (106fe99).

Instead, this PR reverts parts of #11942 and embraces the leading space even when index=False. df.to_string(index=False) will print the leading space when the first column is positive only, as well as preserve leading/trailing spaces on first/last lines.

With the following code:

import pandas as pd
def wrap_to_string(df, **kwargs):
    s = df.to_string(**kwargs)
    print(str(kwargs).center(25, '-'))
    for i, line in enumerate(s.split('\n')):
        print(f'^{line}$-{i}')
    print()
df = pd.DataFrame({'w': [1, 2], 'x': [3, -4], 'y': [555, 666],
                   'z': [777, -888], 'a': ['AAA', '   ']})
cols_ = list(map(list, ['wxyza', 'xyzaw', 'yzawx', 'zawxy', 'awxyz']))
for cols in cols_:
    wrap_to_string(df[cols], index=False)

Output with master:

-----{'index': False}----  # last cell (three spaces) disappeared
^w  x    y    z    a$-0
^1  3  555  777  AAA$-1
^2 -4  666 -888$-2

-----{'index': False}----  # misaligned
^x    y    z    a  w$-0
^3  555  777  AAA  1$-1
^-4  666 -888       2$-2

-----{'index': False}----  # misaligned
^y    z    a  w  x$-0
^555  777  AAA  1  3$-1
^666 -888       2 -4$-2

-----{'index': False}----  # misaligned
^z    a  w  x    y$-0
^777  AAA  1  3  555$-1
^-888       2 -4  666$-2

-----{'index': False}----  # misaligned
^a  w  x    y    z$-0
^AAA  1  3  555  777$-1
^     2 -4  666 -888$-2

Output with this PR:

-----{'index': False}----
^ w  x    y    z    a$-0
^ 1  3  555  777  AAA$-1
^ 2 -4  666 -888     $-2

-----{'index': False}----
^ x    y    z    a  w$-0
^ 3  555  777  AAA  1$-1
^-4  666 -888       2$-2

-----{'index': False}----
^   y    z    a  w  x$-0
^ 555  777  AAA  1  3$-1
^ 666 -888       2 -4$-2

-----{'index': False}----
^   z    a  w  x    y$-0
^ 777  AAA  1  3  555$-1
^-888       2 -4  666$-2

-----{'index': False}----
^   a  w  x    y    z$-0
^ AAA  1  3  555  777$-1
^      2 -4  666 -888$-2

Similar effect on Series as well.

[gfyoung]

Definitely should use pytest.mark.parametrize for this.

[gshiba]

I updated the code style to match other tests in the same file.

[gfyoung]

cc @datapythonista

[codecov]

Codecov Report

Merging #22505 into master will decrease coverage by 0.15%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #22505      +/-   ##
==========================================
- Coverage   92.18%   92.03%   -0.16%     
==========================================
  Files         169      169              
  Lines       50820    50778      -42     
==========================================
- Hits        46850    46735     -115     
- Misses       3970     4043      +73

Flag	Coverage Δ
#multiple	90.44% <100%> (-0.16%)	⬇️
#single	42.22% <0%> (-0.16%)	⬇️

Impacted Files	Coverage Δ
pandas/io/formats/format.py	98.35% <100%> (-0.01%)	⬇️
pandas/io/formats/console.py	65.15% <0%> (-10.61%)	⬇️
pandas/errors/__init__.py	92.3% <0%> (-7.7%)	⬇️
pandas/core/dtypes/base.py	92.68% <0%> (-7.32%)	⬇️
pandas/core/arrays/base.py	88% <0%> (-6.25%)	⬇️
pandas/io/html.py	89.17% <0%> (-2.08%)	⬇️
pandas/io/parquet.py	71.79% <0%> (-1.94%)	⬇️
pandas/io/formats/html.py	88.81% <0%> (-1.87%)	⬇️
pandas/core/apply.py	96.75% <0%> (-1.86%)	⬇️
pandas/core/arrays/datetimelike.py	94.02% <0%> (-1.52%)	⬇️
... and 51 more

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[datapythonista]

lgtm, but I think the changelog needs to be moved to 0.24.0.

@jreback can you take a look and see if you're happy with this?

[jreback]

change looks ok

[jreback]

move to 0.24.0

can you make this more explicit, e.g. say what cases it is fixing.

[jreback]

can you add a comment where the issues that are closed

[pep8speaks]

Hello @gshiba! Thanks for updating the PR.

• There are no PEP8 issues in the file pandas/io/formats/format.py !

• There are no PEP8 issues in the file pandas/tests/io/formats/test_format.py !

[datapythonista]

lgtm, thanks for the fix @gshiba

[jreback]

thanks @gshiba