[jira] [Created] (ARROW-5566) [Python] Overhaul type unification from Python sequence in arrow::py::InferArrowType

["Wes McKinney (JIRA)" <ji...@apache.org>]

Wes McKinney created ARROW-5566:
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             Summary: [Python] Overhaul type unification from Python sequence in arrow::py::InferArrowType
                 Key: ARROW-5566
                 URL: https://issues.apache.org/jira/browse/ARROW-5566
             Project: Apache Arrow
          Issue Type: Improvement
          Components: Python
            Reporter: Wes McKinney


I'm working on ARROW-4324 and there's some technical debt lying in arrow/python/inference.cc because the case where NumPy scalars are mixed with non-NumPy Python scalar values, all hell breaks loose. In particular, the innocuous {{numpy.nan}} is a Python float, not a NumPy float64, so the sequence {{[np.float16(1.5), np.nan]}} can be converted incorrectly. 

Part of what's messy is that NumPy dtype unification is split from general type unification. This should all be combined together with the NumPy types mapping onto an intermediate value (for unification purposes) that then maps ultimately onto an Arrow type



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