API: read_csv,from_csv/to_csv keyword consistency

[rmorgans]

method naming consistency issue #577

• to_csv uses line_terminator and read_csv uses lineterminator
• compression kw ENH: DataFrame.to_csv support for "compression='gzip'" #7615 (ENH: added compression kw to to_csv GH7615 #11219)
• sep/delimiter read_csv/to_csv sep/delimiter inconsistency #7662
• from_csv differs from read_csv DataFrame.from_csv undocumented behavior of index_col #9556 (DOC: clarify purpose of DataFrame.from_csv (GH4191) #10163)
• decimal Add support of 'decimal' option to Series.to_csv and Dataframe.to_csv #8448 (671c4b3)

[jreback]

@rmorgans yep. I created a master issue for things that I recall, but I am sure there are some more. Would you like to do a full comparison of the read_csv/to_csv options to see if there any other conventions that are inconsisten (and include from_csv) here as well.

Ideally we would like to make most consistent name work and deprecate the others. Would you like to do a pull-request?

[Dobatymo]

all other issues referenced here are closed.
only

to_csv uses line_terminator and read_csv uses lineterminator

still applies.

[jreback]

@Dobatymo updated. would you like to do a PR to deprecate line_terminator in .to_csv?

[Dobatymo]

Not sure how to deprecate something. Should I add lineterminator and add to the docs that line_terminator is deprecated? Or directly delete it?

[TomAugspurger]

Not sure how to deprecate something

If you look in pandas/utils/_decorators.py you'll see a deprecate_kwarg. You can use that to and it'll emit a warning if the incorrect version is passed.

We'll also want to

1. update all the docs and tests to use lineterminator
2. Add a new tests that uses line_terminator and checks that the deprecation warning was emitted
3. Add a release note to whatsnew/v0.21.1.txt (@jreback we're OK with adding deprecation warnings in point releases, correct?)

[jorisvandenbossche]

Add a release note to whatsnew/v0.21.1.txt (@jreback we're OK with adding deprecation warnings in point releases, correct?)

Let's keep that for 0.22.0. Introducing deprecation warnings is somehow changing behaviour in the sense that it gives annoying warnings one needs to change code for to get rid of them. I would keep 0.21.1 for essential bug fixes.

But apart from that, actual question: is there a reason we would prefer lineterminator over line_terminator ? (I find the latter more readable)