TST: Fix doctests in style.py

[Leonardofreua]

tl;dr

Fix the numerous doctests that are giving errors in the style.py file:

FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.apply
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.applymap
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.background_gradient
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.hide_columns
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.hide_index
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.highlight_between
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.highlight_quantile
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.pipe
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.set_properties
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.set_table_attributes
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.set_table_styles
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.set_td_classes
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.set_tooltips
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.text_gradient
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.to_latex
FAILED pandas/io/formats/style.py::pandas.io.formats.style.Styler.where
======================================================================== 16 failed, 1 passed, 1 warning in 0.76s ========================================================================

Detailed instructions

Each of the doctests failed for different reasons. You can see the reason for each of them by running the command below:

python -m pytest --doctest-modules pandas/io/formats/style.py

In general, the above errors can be fixed with things like:

• Fixing a typo (a missing comma, a misspelled variable name...)
• Adding an object that hasn't been defined (like, if df is used, but
  no sample dataset df has been first defined)
• Fixing the expected output, when it's wrong
• In exceptional cases, examples shouldn't run, since they can't work.
  For example, a function that connects to a private webservice. In
  such cases, we can add # doctest: +SKIP at the end of the lines
  that should not run
• In some cases, as it is not possible to display the result as it may
  involve the styling of a table, it will be necessary to skip the
  test (ensuring that it is happening correctly) or use the tag # doctest: +ELLIPSIS

Observation

In some cases it'll be necessary to use # doctest: +SKIP and later in another use or in this same issue, add images for some results that cannot be displayed, such as stylizations and color addition (this was dealt with in another issue).

[Leonardofreua]

take

[attack68]

Styler is a different object to the rest of pandas, its methods affect the visual output of browsers and other renderers.

These docstrings were created as a balance between helping the user and being able to read the code as a developer.

Adding images has the disadvantage of being more difficult for developers to edit, but being visually accurate.
Some of the the doc tests as is has the advantages of being editable by devs and visible to users, but the disadvantage of failing a doc test.

The solution here, as is with many styler doc tests is to skip the doc test, where appropriate.

If no output is provided then considerations should be made as to either:

• skip it: no output is required in the context.
• add a textual output and skip the test.
• add an image output and skip the test.

For example background_gradient uses images since the examples produce very specific visual effects that need to be demonstrated, but hide_index does not need such graphics, only textual representation.

[Leonardofreua]

@attack68 Great observations. I think that all doctests I found in the style.py file fit the points you cited.

The methods I have noticed that will need images in your doctests are below:

• apply()
• applymap()
• set_table_styles() maybe?
• set_properties()
• pipe()

[attack68]

@attack68 Great observations. I think that all doctests I found in the style.py file fit the points you cited.

The methods I have noticed that will need images in your doctests are below:

• apply()
• applymap()
• set_table_styles() maybe?
• set_properties()
• pipe()

all of those (except pipe) are extensively covered in the table visualization user guide. It might be more advantageous to redirect users to that page.

The background gradient, in my opinion, is an exception because its docstring shows different combinations of keyword arguments which have different effects, which are not covered in the user guide.

pipe is really functional programming and it might suit to just use textual examples.

[Leonardofreua]

@attack68 Great observations. I'll put a link to the Table visualization for these items. Example below: