Series do not display HTML repr

[ghost]

Not sure if it's always been this way or if refactoring broke something.
In any case it looks strange when in ipnb:

related to #5550, making reprs consistent.

[jtratner]

It's always been that way.

[ghost]

Thought so, it's surprising users haven't flagged this earlier then.

[lexual]

#10300

[smcinerney]

WORKAROUND: Series.to_frame() e.g. df.isnull().sum().to_frame()

[ankostis]

Series should have a different output from Frames. See #10300 (comment)

[smcinerney]

I guess we can't distinguish between a plain dataframe Series e.g. produced by a slice, and a "table-like" series produced by a function like df.isnull().sum(), where the row-indices are actually column names of the df? The latter is really a table in disguise. pandas does this a lot.

[TomAugspurger]

FWIW, I think DataFrames having the column names above, and Series having the name below (perhaps as a caption) should be visually distinct enough.

[big-o]

I've taken an initial stab at this. It's my first contribution to the project so it's probably pretty messy and will need some further work, but if it's the sort of thing you're after and can point me in the right direction of what extra bits are needed then I'm happy to do it.

Here's my fork: https://github.com/big-o/pandas. I haven't submitted a PR yet because it needs unit tests and I don't want to start on that until I'm certain that I'm on the right track functionality-wise.

It doesn't quite support everything that DataFrame.to_html() does (justify and sparsify options aren't implemented) but it hopefully covers the most important bits.

Here's a few screenshots:

[jreback]

would be easier to review as a PR (then we can comment directly on the impl); you can add tests later

[big-o]

would be easier to review as a PR (then we can comment directly on the impl); you can add tests later

Done!