[Python] Add option (or some equivalent) to toggle memory mapping functionality when using parquet.ParquetFile or other read entry points

[asfimport]

See issue described in #1946. When passing a filename to parquet.ParquetFile, one cannot control what kind of file reader internally is created (OSFile or MemoryMappedFile)

Reporter: Wes McKinney / @wesm
Assignee: Wes McKinney / @wesm

PRs and other links:

• GitHub Pull Request #3639

_{Note: This issue was originally created as ARROW-2627. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
You can pass an OSFile or MemoryMappedFile instance to ParquetFile, though, no? If so, I'm not sure it makes sense to add another way for the user to choose the instantiated file reader class.

[asfimport]

Wes McKinney / @wesm:
I think I addressed this, but I will confirm

[asfimport]

Wes McKinney / @wesm:
This was partially added in ARROW-2807 (9769644) but it isn't exposed in ParquetDataset, so I'll add that

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 3639
#3639