How do I declare a field with more than one value type? For example, I'm trying to write a

path

file that can either take a single string or a list of strings (corresponding to the

path

argument in

dask.dataframe.read_parquet

). Separately, the two value types can be written as:

Field(String, …)
Field([String], …)

Is there something like a union type that can combine the two types?

you may want a

Selector

Can you elaborate on how a

Selector

would work in this case? Here's an excerpt of the original code.

"parquet": Permissive({
    "path": Field(String, is_required=True, description="Path to read from."),
    "columns": Field([String], is_required=False, description="Fields names to read in as columns.")
}),

If

Selector

took a list of fields instead of a dict, I could imagine doing something like this.

"parquet": Permissive({
    "path": Field(
        Selector([
            Field(String, is_required=True, description="Path to read from."),
            Field([String], is_required=True, description="List of paths to read from."),
        ]),
        is_required = True,
        description = "Path to read from."
    ),
    "columns": Field([String], is_required=False, description="Fields names to read in as columns.")
}),

Ultimately, I want the path to be valid for a string or a list of strings in its config.

dataframe:
  parquet:
    path: /example/parquet

or

dataframe:
  parquet:
    path:
      - /example/parquet/part0
      - /example/parquet/part1