FutureWarning in Pandas 0.24.0

[iaindillingham]

Pandas 0.24.0 throws a FutureWarning when used with Altair 2.3.0 here, which prevents the chart being rendered correctly. The message:

[my_virtualenv]/lib/python3.6/site-packages/altair/utils/core.py:294: FutureWarning: A future version of pandas will default to `skipna=True`. To silence this warning, pass `skipna=True|False` explicitly.

I notice that Altair's requirements.txt doesn't specify version. Would it be worth doing so?

[afonit]

@iaindillingham I just upgraded to pandas 0.24.0 and am using altair 2.3.0.
I am not getting the error you are seeing, my plots are showing up fine.

What platform are you on?
To confirm from what you said, did you get the error upon import of altair or after import and when plotting data?

[iaindillingham]

Python 3.6 on Ubuntu 18.04. The error was raised when plotting data, not upon import. I'll try and reproduce.

[afonit]

I have now gotten the error.
Interesting - it is happening on some of my plots and not on others. I am trying to narrow it down.

[afonit]

@iaindillingham
So far I can get it to come up if I am not declaring types for the fields.

For example:

x='actual'
vs
x='actual:Q'

Is that the case for you - that if you declare the type you don't get the error?

[jakevdp]

It looks like the warning is in pandas infer_dtype function, which we use in automatically determining the data type when not specified by the user here.

[iaindillingham]

Yes, @afonit that's correct. Although only when I use the shorthand syntax, not when I supply a type kwarg.

[jakevdp]

Fix is to explicitly pass skipna=False in this line: https://github.com/altair-viz/altair/blob/c4495f965db621e8bd0c2b3dd0390ef30ad33456/altair/utils/core.py#L72

We'll have to do it carefully, though, because prior to pandas 0.20.0, infer_dtype takes no keyword arguments.

[jakevdp]

I pushed a fix in #1315