Default values for list fields about fhir.resources HOT 3 CLOSED

TL;DR

What you're suggesting is already taken care of automatically by Pydantic.

Verbose Explanation

This really comes down to how Pydantic uses the "default" value. If you take a look at the docstring for that field, you'll notice that what that parameter is actually allowing you to do is replace the default value, not set it.

For example, look at the definition of the careTeam field of a Claim:

careTeam: ListType[fhirtypes.ClaimCareTeamType] = Field(
    None,
    alias="careTeam",
    title="Members of the care team",
    description="The members of the team who provided the products and services.",
    # if property is element of this resource.
    element_property=True,
)

Because careTeam is a ListType (which is an alias for the Python typing.List type), Pydantic will automatically assign it a default value of []. The cardinality of this field is of course 0..* in the FHIR spec, meaning it is optional but can also have many values.

If we were to change the default parameter to Field() from None to [], that would tell Pydantic to overwrite the default from [] to [], which doesn't accomplish much.

And just to round out this discussion, for fields with cardinality 1..1 (like the created field of the Claim FHIR type), we pass the ellipsis (...) to tell Pydantic that we don't want to overwrite the default value, but there must be some value present.

from fhir.resources.

Look at:

from fhir.resources.patient import Patient
list(Patient.element_properties())

it prints:

....
ModelField(name='name', type=Optional[List[HumanNameType]], required=False, default=None)
...

Yet, the field itself has the declaration:

name: ListType[fhirtypes.HumanNameType] = Field(

And calling print(Patient().name) gives None.
Hence, what you are saying is not what actually happen.

from fhir.resources.

A little late, but I'll reply since it's still open. Just to echo @ItayGoren 's comment, having a default=None will make that list default to None rather than []. Even though it's typed as ListType[fhirtypes.ClaimCareTeamType] it will be automatically converted to a Optional[ListType[fhirtypes.ClaimCareTeamType]] if the default is None.

If the desired behavior is to have that field default to an empty list, we'd have to use pydantic.Field(default_factory=list)

from fhir.resources.