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wend.pydantic

Pydantic integration (optional dependency: pip install 'wend[pydantic]').

Two kinds of field metadata, for typing.Annotated:

  • PathOf(expr): the field holds a path of expr's layout. A path given as input must match expr; bindings given as input (a mapping, or an object such as another model) are rendered through it, which resolves the path at validation time, as Pydantic's ImportString imports. Either way, expr's preconditions (requires) are then checked against the filesystem::

    class Job(BaseModel): shard: Annotated[Path, PathOf(shard.requires(File, Exists))] last: Annotated[Match, PathOf(shard)] # the path and its bindings

  • wend's conditions themselves (File, Dir, Exists, Absent, Readable, Writable, Creatable, Listable, and Under with a static base) validate a path field: Annotated[Path, File, Exists] is Pydantic's FilePath. They work without importing this module, which they load when Pydantic asks for their schema.

The field's type decides the validated value: Path (or another PurePath class), str, or Match for the path with its bindings. In JSON, every one of them is the path string.

Checks touch the filesystem when the model is validated, and describe it at that moment (docs/SEMANTICS.md ยง10): validation is an effect here.

PathOf 

PathOf(expr: Any)

Field metadata: the value is a path of expr (an expression, a union, or anything P takes).

  • A path (str, os.PathLike or Match) must have exactly one reading by expr; no reading and several readings are validation errors.
  • Anything else is bindings (see wend.bindings), rendered through expr. Defaults apply as they do in render.

Then expr's preconditions are checked with the bindings (PathExpr.check); a Match result carries those bindings.

expr instance-attribute 

expr: PathExpr | PathUnion = (
    expr if isinstance(expr, PathUnion) else _coerce(expr, at_head=True)
)

validate 

validate(value: Any) -> tuple[str, Match]

The path value stands for and its reading, or a PydanticCustomError. A declaration that cannot be used this way (NotInvertibleError) is raised as it is.