BUG: added missing fill_na parameter to DataFrame.unstack() with list of levels

[tanmay1618]

• closes DataFrame.unstack() with list of levels ignores fill_value #30740
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[pep8speaks]

Hello @tanmay1618! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2020-01-09 18:09:40 UTC

[WillAyd]

Thanks for the PR. Does this fix a particular issue? If so will want to add tests first and foremost

[tanmay1618]

Yes, it fixes this issue. #30740. Sure, I will add tests for this.

[simonjayhawkins]

@tanmay1618 Thanks for the PR. generally lgtm. can you add a whatsnew under bugfixes.

[tanmay1618]

getting this error on running tests

pandas/__init__.py:54: in <module>
    from pandas.core.api import (
pandas/core/api.py:4: in <module>
    from pandas._libs.missing import NA
E   ImportError: cannot import name 'NA' from 'pandas._libs.missing'

[TomAugspurger]

@tanmay1618 you probably need to rebuild the C extensions. python setup.py build_ext -i.

[simonjayhawkins]

Thanks @tanmay1618 for the changes. a few nits. ping on green

[simonjayhawkins]

Thanks @tanmay1618 for this PR. lgtm pending green.

[tanmay1618]

@simonjayhawkins Thanks for all the help, change requests and helping out through the PR. The checks are all green, now.

[tanmay1618]

@TomAugspurger Thanks for all your suggestions and help as well.

[TomAugspurger]

Thanks @tanmay1618!