BUG: Fix skipna default value in method signatures

[jhlegarreta]

Set skipna default values to True so that the value matches the
purpose of the variable and its docstring.

• closes DOC: Dataframe.skew invalid function signature for "skipna" #34063
• tests added / passed
• Ensure all linting tests pass, see here for how to run them
• whatsnew entry

[jhlegarreta]

I did not change the mad method, since its signature matches the docstring and the implementation. Changing that one would require a deprecation cycle I guess; if not, let me know and I will amend the commit.

[jreback]

I did not change the mad method, since its signature matches the docstring and the implementation. Changing that one would require a deprecation cycle I guess; if not, let me know and I will amend the commit.

yeah this is fine

[jreback]

looks fine. @jbrockmendel ok here?

[jbrockmendel]

could remove the if skipna is None in _stat_function

[jhlegarreta]

could remove the if skipna is None in _stat_function

Realizing here that I may have left behind many of them in private functions, e.g.

https://github.com/pandas-dev/pandas/pull/43980/files#diff-1a2e3df0db7dd8bddc2ec4bff9de8a7a55e328e6c32e2cecde761dc9549fcd46R10390
https://github.com/pandas-dev/pandas/pull/43980/files#diff-1a2e3df0db7dd8bddc2ec4bff9de8a7a55e328e6c32e2cecde761dc9549fcd46R10443
https://github.com/pandas-dev/pandas/pull/43980/files#diff-1a2e3df0db7dd8bddc2ec4bff9de8a7a55e328e6c32e2cecde761dc9549fcd46R10509
https://github.com/pandas-dev/pandas/pull/43980/files#diff-1a2e3df0db7dd8bddc2ec4bff9de8a7a55e328e6c32e2cecde761dc9549fcd46R10553

etc. There are still 10 (+2 corresponding to the sem method) appearances.

Are these 10 supposed to be changed as well ?

[jhlegarreta]

@jreback @jbrockmendel any suggestion as to what I should do concerning #43980 (comment) ? Thanks.

[jreback]

@jreback @jbrockmendel any suggestion as to what I should do concerning #43980 (comment) ? Thanks.

see if you break anything by changing them. IIRC we did this for some backwards compat but that was quite a while ago.

[jhlegarreta]

see if you break anything by changing them. IIRC we did this for some backwards compat but that was quite a while ago.

👍 Push-forced in e15a1ce. Let's see what the CIs say.

[jreback]

thanks @jhlegarreta very nice!