[Python] pa.union() mode argument unintuitive

[asfimport]

>>> pa.union([pa.field('x', pa.int16())], 'sparse')
UnionType(union[dense]<x: int16=0>)
>>> pa.union([pa.field('x', pa.int16())], 'dense')
UnionType(union[dense]<x: int16=0>)
>>> pa.union([pa.field('x', pa.int16())], 42)
UnionType(union[dense]<x: int16=0>)

I would suggest allowing "sparse" and "dense" strings as aliases to the internal enum values, and disallowing everything else.

Reporter: Antoine Pitrou / @pitrou
Assignee: Antoine Pitrou / @pitrou

PRs and other links:

• GitHub Pull Request #1778

_{Note: This issue was originally created as ARROW-2341. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 1778
#1778