pyrixos-espalier

Data models validated from type annotations, in Python with no compiled code and no dependencies. Espalier implements the part of the pydantic 2 API that typed configuration files and wire formats use, so code written against that part runs with from espalier import ... in place of from pydantic import ....

PyrixOS uses it in Lattice, Cloche and Trellis, so that its build tools install without Rust or C extensions.

pip install pyrixos-espalier

from typing import Annotated, Literal

from espalier import BaseModel, ConfigDict, Field, ValidationError


class Mount(BaseModel):
    model_config = ConfigDict(frozen=True, extra="forbid", strict=True)

    source: str = Field(min_length=1)
    target: str
    mode: Literal["ro", "rw"] = "ro"
    size: Annotated[int, Field(ge=0)] = 0


mount = Mount.model_validate_json('{"source": "/a", "target": "/b"}')
print(mount.model_dump_json())  # {"source":"/a","target":"/b","mode":"ro","size":0}

try:
    Mount(source="", target="/b", size=-1)
except ValidationError as error:
    print(error)

What it supports

• BaseModel with model_validate, model_validate_json, model_dump, model_dump_json, model_copy, model_construct, model_rebuild, model_fields, model_fields_set, model_extra and model_computed_fields. Models compare equal by class and fields, frozen models hash, and models copy and pickle.
• ConfigDict keys frozen, extra (ignore, forbid, allow), strict, alias_generator, populate_by_name, validate_by_name, validate_by_alias, serialize_by_alias, arbitrary_types_allowed and title. A subclass's config is merged over its bases'.
• Field with defaults, default factories, aliases, exclude, repr, strict, discriminator and the constraints gt, ge, lt, le, multiple_of, min_length, max_length and pattern, as a default or inside Annotated.
• field_validator (before, after, plain), model_validator (before, after, wrap), BeforeValidator, AfterValidator, PlainValidator, PlainSerializer and computed_field. Validators may take a ValidationInfo with mode, field_name and data.
• TypeAdapter for any supported type, with validate_python, validate_json, dump_python and dump_json.
• The types int, float, str, bool, bytes, None, Any, enums, Literal, unions, Optional, discriminated unions, datetime.datetime, datetime.date, pathlib paths, list, tuple (fixed and variable length), set, frozenset, dict, Mapping, type[...], NewType, type aliases, nested and recursive models and forward references. Other classes are checked with isinstance.
• Strict and lax modes with pydantic's conversion rules, including JSON input in strict mode giving lists for tuples and sets, and strings for enums and datetimes. strict= on a validate call replaces the strict of the model's config and of the models in it.
• ValidationError, a ValueError, with pydantic's error types, locations and messages and the same text layout.

Differences from pydantic

• No JSON Schema generation, no BaseSettings, no dataclass support, no generic models, and no context passed to validators.
• The error for invalid JSON quotes Python's json module, and other parse errors (datetime, date) quote the standard library's message.
• Error text has no documentation link lines.
• A UTC datetime read from JSON has datetime.timezone.utc as tzinfo.
• An instance given where a model is expected is used as it is, not revalidated, as with pydantic's default revalidate_instances.
• Validation runs in Python. Validating or dumping a model is about 5 to 7 times slower than with pydantic-core; for configuration files and protocol messages this is well under a millisecond each.

Migrating from pydantic

Replace pydantic with espalier in imports, and pydantic.alias_generators with espalier.alias_generators. Code that sets __pydantic_*__ attributes or calls pydantic-core directly needs changes; Espalier never calls a nested model's __init__, so a model that overrides __init__ is validated by its outer model without it.

Development

pip install --group dev
pip install -e .
pybootstrap check

The tests record the types and messages pydantic gives for the same input.

License

GPL-2.0-only. See LICENSE.