ARROW-5258 / https://github.com/apache/arrow/pull/4236 it is now possible to collect the file metadata while writing different files (then how to write those metadata was not yet addressed -> original issue ARROW-1983).
However, currently, the file_path information in the ColumnChunkMetaData object is not set. This is, I think, expected / correct for the metadata as included within the single file; but for using the metadata in the combined dataset `_metadata`, it needs a file path set.
So if you want to use this metadata for a partitioned dataset, there needs to be a way to specify this file path.
Ideas I am thinking of currently: either, we could specify a file path to be used when writing, or expose the `set_file_path` method on the Python side so you can create an updated version of the metadata after collecting it.