typedattr 0.1.8

Typed conversion of dictionaries to attrs instances

typedattr

Typechecking and conversion utility for attrs.

Parses a dictionary into an attrs instance. Contains other generic object, type and cache utilities.

Install

Requires python 3.7 or higher.

pip install typedattr

Quickstart

Define class hierarchy and parse the input.

from attrs import define
from typing import Optional
from typedattr import attrs_from_dict

@define
class Cfg:
    foo: int = 12
    bar: Optional[int] = None

print(attrs_from_dict(Cfg, {"foo": 1, "bar": 2}))
# Cfg(foo=1, bar=2)


@define
class CfgNested:
    sub_cfg: Cfg = None

print(attrs_from_dict(CfgNested, {"sub_cfg": {"foo": 1, "bar": 2}}))
# CfgNested(sub_cfg=Cfg(foo=1, bar=2))

Features

• Nested checking and conversion of python standard types.
• @definenumpy decorator for equality check if the instances contains numpy arrays.
• Supports old and new style typing (e.g. typing.List and list)
• Supports positional and keyword arguments in classes.
• Can typecheck existing attrs instances.
• Allows custom conversions, by default converts source type str to target type Path and int to float.
• Allows to redefine which objects will be recursed into, by default recurses into standard containers (list, dict, etc.)

Strict mode (default)

• Convert everything to the target type, e.g. if the input is a list and the annotation is a tuple, the output will be a tuple.
• Raise errors if types cannot be matched, there are unknown fields in the input or abstract annotation types are used (e.g. Sequence).

Non-strict mode

Enabled by calling attrs_from_dict with strict=False

• No conversion except for creating the attrs instance from the dict.
• Ignore silently if types cannot be matched or abstract annotation types are used.
• Warn about unknown fields in the input.

Hints

The following behaviour stems from the attrs package:

• New attributes cannot to be added after class definition to an attrs instance, unless it is created with @define(slots=False). Explanation
• Untyped fields or "ClassVar" typed fields will be ignored by @attrs.define and therefore also by this library.

Possible improvements

• Supports Callable but does not typecheck the signature
• Not tested for NewType, Literal

Install locally and run tests

Clone repository and cd into, then:

pip install -e .
pip install pytest pytest-cov pylint
pylint typedattr

# run tests for python>=3.7
python -m pytest --cov
pylint tests

# run tests for python>=3.9
python -m pytest tests_py39 --cov
pylint tests_py39

Alternatives

This library should be useful for off-the-shelf typechecking and conversion of dicts to attrs instances.

For more complex use cases there are many alternatives: cattrs, attrs-strict, pydantic, dataconf to name a few.