BUG: Float64Index getitem raises error with tuple-like values

[jorisvandenbossche]

So when you have a Series with the combination of a Float64Index and tuple values, getitem/[] gives an error:

In [46]: s = pd.Series([1,2,3], index=[0.0,0.1,0.2])

In [47]: s[0.0]
Out[47]: 1

In [48]: s = pd.Series([(1,1),(2,2),(3,3)], index=[0.0,0.1,0.2])

In [49]: s[0.0]
...
TypeError: len() of unsized object

When the values are not tuples, or when you have a regular index, or when using ix/loc/iloc this issue does not appear.

This issue is coming from geopandas (geopandas/geopandas#351), where a Series of Point geometries give the same error:

In [66]: import shapely.geometry

In [67]: s = pd.Series([(1,1),(2,2),(3,3)], index=[0.0,0.1,0.2])

In [68]: s = s.map(shapely.geometry.Point)

In [69]: s
Out[69]:
0.0    POINT (1 1)
0.1    POINT (2 2)
0.2    POINT (3 3)
dtype: object

In [70]: s[0.0]
...
TypeError: len() of unsized object

[bkandel]

I did a bit of digging and I think I found the issue. Float64Index.get_value tries to construct a Series with its result if the result is not scalar. A scalar cannot be given as the index for a new Series, so the construction of the series fails. This switch in particular seems problematic: https://github.com/pydata/pandas/blob/master/pandas/indexes/numeric.py#L303

I can't figure out what that switch is trying to do. Even if the resulting value is not a scalar, it seems to me like it should still be treated like any other value that would be retrieved from a Series and simply returned, not used to construct a new Series. Codecov reports that this switch is not tested: https://codecov.io/gh/pydata/pandas/src/8131b5151e10f1a5863ccadef739c21320830f54/pandas/indexes/numeric.py#L306 So it's difficult for me to figure out what the intended function of this code is.

I would propose to simply take out the switch and always return the retrieved value. Any objections?

[jreback]

generally if the indexer returns a single value then it IS the result and you won't contruct a new series

[bkandel]

That's what I thought too. I'll change it and add tests.