DOC: Fix docstrings lack of punctuation

[martinagvilas]

• xref DOC: Fix formatting errors in docstrings #27977
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

Similar to issue #27979, and as pointed out by @datapythonista, the summaries of some dosctrings don’t end with a period.

I added the period to the following cases:

• pandas.IndexSlice •	pandas.MultiIndex.names •	pandas.MultiIndex.is_lexsorted •	pandas.MultiIndex.reorder_levels •	pandas.DatetimeIndex.snap •	pandas.DatetimeIndex.to_perioddelta •	pandas.DatetimeIndex.to_pydatetime •	pandas.DatetimeIndex.to_series •	pandas.TimedeltaIndex •	pandas.PeriodIndex.is_leap_year •	pandas.api.extensions.ExtensionArray._concat_same_type •	pandas.api.extensions.ExtensionArray.dropna 

These are the outputs of validate_docstrings.py when evaluating each case:

pandas.IndexSlice

4 Errors found:	Examples do not pass tests	flake8 error: E231 missing whitespace after ',' (4 times)	flake8 error: E902 TokenError: EOF in multi-line statement	flake8 error: E999 SyntaxError: invalid syntax 1 Warnings found:	No extended summary found 

pandas.MultiIndex.names

3 Warnings found:	No extended summary found	See Also section not found	No examples section found 

pandas.MultiIndex.is_lexsorted

1 Errors found:	Return value has no description 3 Warnings found:	No extended summary found	See Also section not found	No examples section found 

pandas.MultiIndex.reorder_levels

2 Errors found:	Parameters {order} not documented	Return value has no description 3 Warnings found:	No extended summary found	See Also section not found	No examples section found 

pandas.DatetimeIndex.snap

2 Errors found:	Parameters {freq} not documented	Return value has no description 3 Warnings found:	No extended summary found	See Also section not found	No examples section found 

pandas.DatetimeIndex.to_perioddelta

5 Errors found:	Summary should fit in a single line	Parameters {**kwargs, *args} not documented	Unknown parameters {freq}	Parameter "freq" has no description	Return value has no description 2 Warnings found:	See Also section not found	No examples section found 

pandas.DatetimeIndex.to_pydatetime

4 Errors found:	Summary should fit in a single line	Parameters {**kwargs, *args} not documented	The first line of the Returns section should contain only the type, unless multiple values are being returned	Return value has no description 2 Warnings found:	See Also section not found	No examples section found 

pandas.DatetimeIndex.to_series

2 Errors found:	Summary should fit in a single line	Return value has no description 2 Warnings found:	See Also section not found	No examples section found 

pandas.TimedeltaIndex

3 Errors found:	Summary should fit in a single line	Parameters {dtype, verify_integrity, periods, copy, data} not documented	Unknown parameters {periods , copy , data } 1 Warnings found:	No examples section found 

pandas.PeriodIndex.is_leap_year

3 Warnings found:	No extended summary found	See Also section not found	No examples section found 

pandas.api.extensions.ExtensionArray._concat_same_type

2 Errors found:	Parameter "to_concat" has no description	Return value has no description 3 Warnings found:	No extended summary found	See Also section not found	No examples section found 

pandas.api.extensions.ExtensionArray.dropna

2 Errors found:	The first line of the Returns section should contain only the type, unless multiple values are being returned	Return value has no description 3 Warnings found:	No extended summary found	See Also section not found	No examples section found 

I would be happy to also work on the other errors/warnings in this PR on another.

[datapythonista]

lgtm, great job @martinagvilas, and thanks for taking care of those.

[jorisvandenbossche]

@martinagvilas Thanks a lot!