Replace pydantic with attrs + cattrs

.pre-commit-config.yaml

@@ -42,7 +42,8 @@ repos:
       - id: mypy
         args: []
         additional_dependencies:
-          - pydantic
+          - attrs
+          - cattrs
 
 ci:
   autoupdate_schedule: "quarterly"

CHANGELOG.md

@@ -7,6 +7,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Changed
+
+- Replaced the `pydantic` dependency with `attrs` + `cattrs`. The public spec
+  classes (`InfoSpec`, `PackageSpec`, `PyodideLockSpec`) are now `attrs` classes.
+  Construct them from dictionaries with `PyodideLockSpec.from_dict(...)` (and the
+  equivalent `from_dict` on the other specs) instead of `PyodideLockSpec(**data)`,
+  and serialize with `.to_dict()` instead of `.model_dump()`.
+
 ## [0.1.3] - 2026-04-21
 
 ### Changed

pyodide_lock/spec.py

@@ -1,57 +1,90 @@
+import copy
 import json
 from pathlib import Path
-from typing import Literal
+from typing import Any, Literal
 
-from pydantic import BaseModel, ConfigDict, Field
+import attrs
+import cattrs
+from attrs import define, field
+from cattrs.gen import make_dict_structure_fn, make_dict_unstructure_fn, override
 
 
-class InfoSpec(BaseModel):
-    arch: Literal["wasm32", "wasm64"] = "wasm32"
+class SpecValidationError(ValueError):
+    """Raised when a lock spec fails validation."""
+
+
+@define
+class InfoSpec:
     platform: str
-    # This field is deprecated and will not be included in the output
-    version: str = Field(default="0.0.0", exclude=True)
     python: str
+    arch: Literal["wasm32", "wasm64"] = "wasm32"
+    # This field is deprecated and will not be included in the output
+    version: str = field(default="0.0.0", metadata={"exclude": True})
     abi_version: str | None = None
-    model_config = ConfigDict(extra="forbid")
+
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> "InfoSpec":
+        return _converter.structure(data, cls)
+
+    def to_dict(self) -> dict[str, Any]:
+        return _converter.unstructure(self)
 
 
-class PackageSpec(BaseModel):
+@define
+class PackageSpec:
     name: str
     version: str
-    file_name: str = Field(
-        description="Path (or URL) to wheel.",
-    )
+    #: Path (or URL) to wheel.
+    file_name: str
     install_dir: str
     sha256: str = ""
     package_type: Literal[
         "package", "cpython_module", "shared_library", "static_library"
     ] = "package"
-    imports: list[str] = []
-    depends: list[str] = []
+    imports: list[str] = field(factory=list)
+    depends: list[str] = field(factory=list)
     unvendored_tests: bool = False
     # This field is deprecated and will not be included in the output
-    shared_library: bool = Field(default=False, exclude=True)
-    model_config = ConfigDict(extra="forbid")
+    shared_library: bool = field(default=False, metadata={"exclude": True})
 
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> "PackageSpec":
+        return _converter.structure(data, cls)
 
-class PyodideLockSpec(BaseModel):
+    def to_dict(self) -> dict[str, Any]:
+        return _converter.unstructure(self)
+
+
+@define
+class PyodideLockSpec:
     """A specification for the pyodide-lock.json file."""
 
     info: InfoSpec
     packages: dict[str, PackageSpec]
-    model_config = ConfigDict(extra="forbid")
 
     @classmethod
     def from_json(cls, path: Path) -> "PyodideLockSpec":
         """Read the lock spec from a json file."""
         with path.open("r", encoding="utf-8") as fh:
             data = json.load(fh)
-        return cls(**data)
+        return cls.from_dict(data)
+
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> "PyodideLockSpec":
+        """Build a lock spec from a dictionary."""
+        return _converter.structure(data, cls)
+
+    def to_dict(self) -> dict[str, Any]:
+        return _converter.unstructure(self)
+
+    def clone(self) -> "PyodideLockSpec":
+        """Return a deep copy of this lock spec."""
+        return copy.deepcopy(self)
 
     def to_json(self, path: Path, indent: int | None = None) -> None:
         """Write the lock spec to a json file."""
         with path.open("w", encoding="utf-8") as fh:
-            model_dict = self.model_dump()
+            model_dict = self.to_dict()
             json_str = json.dumps(model_dict, indent=indent, sort_keys=True)
             fh.write(json_str)
 
@@ -87,3 +120,36 @@ def check_wheel_filenames(self) -> None:
                 for name, errs in errors.items()
             )
             raise ValueError(error_msg)
+
+
+# ---------------------------------------------------------------------------
+# (de)serialization (attrs + cattrs)
+# ---------------------------------------------------------------------------
+
+
+def _exclude_overrides(cls: type) -> dict[str, Any]:
+    return {
+        f.name: override(omit=True)
+        for f in attrs.fields(cls)
+        if f.metadata.get("exclude")
+    }
+
+
+_converter = cattrs.Converter(detailed_validation=False)
+
+for _cls in (InfoSpec, PackageSpec, PyodideLockSpec):
+    _converter.register_structure_hook(
+        _cls,
+        make_dict_structure_fn(
+            _cls,
+            _converter,
+            _cattrs_forbid_extra_keys=True,
+        ),
+    )
+
+# Some fields are deprecated and excluded from the serialized output.
+for _cls in (InfoSpec, PackageSpec):
+    _converter.register_unstructure_hook(
+        _cls,
+        make_dict_unstructure_fn(_cls, _converter, **_exclude_overrides(_cls)),
+    )

pyodide_lock/utils.py

@@ -182,7 +182,7 @@ def add_wheels_to_spec(
         not 100% reliable, because it ignores any extras and does not do any
         sub-dependency or version resolution.
     """
-    new_spec = lock_spec.model_copy(deep=True)
+    new_spec = lock_spec.clone()
     if not wheel_files:
         return new_spec
     wheel_files = [f.resolve() for f in wheel_files]
@@ -214,7 +214,7 @@ def _fix_new_package_deps(
     from packaging.utils import canonicalize_name
 
     requirements_with_extras = []
-    marker_environment = _get_marker_environment(**lock_spec.info.model_dump())
+    marker_environment = _get_marker_environment(**lock_spec.info.to_dict())
     for package in new_packages.values():
         # add any requirements to the list of packages
         our_depends = []
@@ -264,7 +264,7 @@ def _fix_extra_dep(
 
     requirements_with_extras = []
 
-    marker_environment = _get_marker_environment(**lock_spec.info.model_dump())
+    marker_environment = _get_marker_environment(**lock_spec.info.to_dict())
     extra_package_name = canonicalize_name(extra_req.name)
     if extra_package_name not in new_packages:
         return []
@@ -386,7 +386,7 @@ def package_spec_from_wheel(path: Path, info: InfoSpec) -> PackageSpec:
         sha256=_generate_package_hash(path),
         package_type="package",
         install_dir="site",
-        imports=parse_top_level_import_name(path),
+        imports=parse_top_level_import_name(path) or [],
         depends=[],
     )
 

pyodide_lock/uv_pip_compile.py

@@ -15,10 +15,12 @@
 from typing import TYPE_CHECKING, Any
 from urllib import parse, request
 
+import attrs
+import cattrs
 import pkginfo
+from attrs import define, field
 from packaging.requirements import Requirement
 from packaging.utils import NormalizedName, canonicalize_name
-from pydantic import BaseModel, Field
 
 from .spec import PackageSpec, PyodideLockSpec
 from .utils import add_wheels_to_spec, logger
@@ -94,7 +96,8 @@ def _find_uv_path() -> Path | None:  # pragma: no cover
     return None
 
 
-class UvPipCompile(BaseModel):
+@define
+class UvPipCompile:
     """Update a partial Pyodide distribution with ``uv pip compile``."""
 
     # input/output #############################################################
@@ -109,34 +112,39 @@ class UvPipCompile(BaseModel):
     #: indent level for output lock
     indent: int | None = None
     #: if given, preserve remote URLs starting with these prefixes
-    preserve_url_prefixes: list[str] = Field(default_factory=list)
+    preserve_url_prefixes: list[str] = field(factory=list)
     #: if given, rewrite all missing local wheels with this URL prefix
     base_url_for_missing: str | None = None
 
     # packages #################################################################
     #: list of PEP-508 specs to include when solving
-    specs: list[str] = Field(default_factory=list)
+    specs: list[str] = field(factory=list)
     #: list of local wheels to include when solving
-    wheels: list[Path] = Field(default_factory=list)
+    wheels: list[Path] = field(factory=list)
     #: list of PEP-508 specs to constrain when solving
-    constraints: list[str] = Field(default_factory=list)
+    constraints: list[str] = field(factory=list)
     #: list of PEP-508 specs to exclude from solving
-    excludes: list[str] = Field(default_factory=list)
+    excludes: list[str] = field(factory=list)
 
     # solver ###################################################################
     #: the ``uv`` python platform for pyodide
     python_platform: str = DEFAULT_UV_PYODIDE_PLATFORM
     #: the ``uv`` binary
-    uv_path: Path | None = Field(default_factory=_find_uv_path)
+    uv_path: Path | None = field(factory=_find_uv_path)
     #: extra arguments to ``uv pip compile``
-    extra_uv_args: list[str] = Field(default_factory=list)
+    extra_uv_args: list[str] = field(factory=list)
 
     # misc #####################################################################
     #: a working directory; if unset, uses a temp folder, cleaned on success
     work_dir: Path | None = None
     #: increase logging level while updating
     debug: bool | None = None
 
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> UvPipCompile:
+        """Build from a dictionary, ignoring any unknown keys."""
+        return _converter.structure(data, cls)
+
     def update(self) -> PyodideLockSpec:
         """Update a lock with ``uv pip compile``, managing logging and work folder."""
         old_log_level = logger.level
@@ -425,7 +433,8 @@ def validate_depends(self, lock_spec: PyodideLockSpec) -> None:
             raise InvalidPyodideLockError(msg)
 
 
-class Pep751Toml(BaseModel):
+@define
+class Pep751Toml:
     """A PEP-751 ``pylock.toml``."""
 
     #: the path on disk
@@ -463,7 +472,8 @@ def from_uv_pip_compile(
         return cls(path=path)
 
 
-class Pep508Text(BaseModel):
+@define
+class Pep508Text:
     """A ``requirements.txt``-style file for requirements, constraints, excludes, etc."""
 
     #: the path on disk
@@ -475,7 +485,7 @@ class Pep508Text(BaseModel):
     def text(self) -> str:
         return "\n".join(sorted(self.specs.values()))
 
-    def model_post_init(self, _context: Any) -> None:
+    def __attrs_post_init__(self) -> None:
         """Write the validated specs out to disk."""
         self.path.parent.mkdir(parents=True, exist_ok=True)
         text = self.text
@@ -499,3 +509,11 @@ def from_raw_specs(
                     specs[name] = spec
 
         return specs
+
+
+# The module uses ``from __future__ import annotations``; resolve string
+# annotations so cattrs can build a structure hook for ``UvPipCompile``.
+attrs.resolve_types(UvPipCompile, globalns=globals())
+
+#: extra keys are ignored when structuring (mirrors the previous pydantic default)
+_converter = cattrs.Converter()

pyproject.toml

@@ -12,7 +12,8 @@ readme = "README.md"
 requires-python = ">=3.12"
 dependencies = [
     # compatible with pyodide-build and the as-shipped wheel in the pyodide distribution
-    "pydantic>=2",
+    "attrs",
+    "cattrs",
 ]
 classifiers = [
     "Programming Language :: Python :: 3",
@@ -69,7 +70,6 @@ python_version = "3.10"
 mypy_path = ["pyodide_lock", "tests"]
 show_error_codes = true
 warn_unreachable = true
-plugins = ["pydantic.mypy"]
 
 check_untyped_defs = true
 ignore_missing_imports = true

tests/conftest.py

@@ -76,7 +76,7 @@ def example_lock_data():
 
 @pytest.fixture
 def example_lock_spec():
-    return PyodideLockSpec(**deepcopy(LOCK_EXAMPLE))
+    return PyodideLockSpec.from_dict(deepcopy(LOCK_EXAMPLE))
 
 
 # build a wheel