BUG: If Series is called with no arguments, let it have a RangeIndex (#16737)

[alanbato]

• closes Unexpected results creating an empty Series #16737
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

Before:

In [4]: Series().index
Out[4]: Index([], dtype='object')

Now:

In [3]: Series().index
Out[3]: RangeIndex(start=0, stop=0, step=1)

[jreback]

make a less verbose comment, like:

Series constructor will default to construct a RangeIndex, rather than an Index when constructed as empty.

[jreback]

needs a test

[alanbato]

Should I add the test code in the following test? Or somewhere else?
Is setting check_index_type=True enough?

def test_constructor_empty(self):
        empty = Series()
        empty2 = Series([])

        # the are Index() and RangeIndex() which don't compare type equal
        # but are just .equals
        assert_series_equal(empty, empty2, check_index_type=False)

        empty = Series(index=lrange(10))
        empty2 = Series(np.nan, index=lrange(10))
        assert_series_equal(empty, empty2)

[jreback]

you prob just need to remove the check_index_type=False and then your change should work

[jreback]

can you rebase and respond to comments

[TomAugspurger]

I would prefer to see this go the other way, so that pd.Series([]).index and pd.Series().index are both an empty Index with object dtype. Then we'll have a consistent rule of "empty = object dtype"

[alanbato]

I also think we should aim for consistency, I'll change the code accordingly so pd.Series([]).index and pd.Series().index evaluate to an empty Index.

[jreback]

revisiting this, can you rebase and update and we can review

[alanbato]

Hmmm, I think I messed up the rebase. Uhm. What should I do?

[TomAugspurger]

@alanbato we should be able to recover it from your local git reflog, and then do the rebase again.

Ping one of us on gitter at https://gitter.im/pydata/pandas and we'll walk you through it.

[jorisvandenbossche]

Your actual commit is still in this branch, so a git fetch upstream and git rebase -i upstream/master and then only keeping the commit you want should also work. But as @TomAugspurger said, feel free to ping on gitter as well for help.

[alanbato]

I think I did it! Thanks for your help @TomAugspurger @jorisvandenbossche.
But the question still stands, what should be the expected behaviour?

Also pinging @jreback in case he has something to say

Cheers! 🐍

[jorisvandenbossche]

I also think we should aim for consistency, I'll change the code accordingly so pd.Series([]).index and pd.Series().index evaluate to an empty Index.

I think we agree on this one (so what @TomAugspurger proposed)

[jreback]

closing as stale, if you want to work on this, pls ping.