Python: All none-Pandas column should be converted to NullArray

[asfimport]

At the moment we throw ArrowException: Type error: Unable to infer type of object array, were all null but for this case we have NullArray inside of Arrow.

Reporter: Uwe Korn / @xhochy
Assignee: Wes McKinney / @wesm

Related issues:

• Arrow 0.3 release (blocks)

_{Note: This issue was originally created as ARROW-707. Please see the migration documentation for further details.}

[asfimport]

Uwe Korn / @xhochy:
@wesm is that ok with you? I think the other way round could be a bit more complicated as we could either convert to a float-array of NaNs or an object array full of None.

[asfimport]

Wes McKinney / @wesm:
Sounds good to me

[asfimport]

Wes McKinney / @wesm:
I made this a blocker for 0.3. @robertnishihara @pcmoritz I noticed you have some NullArray-specific stuff in Ray, are there some missing features in Arrow that you need?

[asfimport]

Wes McKinney / @wesm:
PR: #554

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 554
#554