python-attrs / python-attrs/cattrs

Natively support more types with pre-defined optional hooks

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#641 3 comments 0 reactions 0 assignees View on GitHub

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enhancement
Dominant language
Python
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Merged PRs (30d)
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Description

cattrs comes with a rich set of converters, but the variety of types supported by those converters out of the box is limited. Adding custom structure/unstructure hooks is pretty straightforward and well documented, and in most cases could be as trivial as in the example below. However, as an end user, I would be happy to have something even more simple, something that I wouldn't copy-paste from one project to another :)

A few ideas come to my mind:

  1. What about adding a standalone function or a Converter method register_extra_hooks(converter, cls, structure=True, unstructure=True) (and its variant without first argument, defaulting to global_converter) that will cover less frequently used types from stdlib, like uuid, zoneinfo, ipaddress, re.Pattern, etc? This won't require any overhead in default case, but will enable one liner
register_extra_hooks(converter, ZoneInfo)

instead of

@converter.register_structure_hook
def structure_zoneinfo(value: Any, _) -> ZoneInfo:
    return ZoneInfo(str(value))

@converter.register_unstructure_hook
def unstructure_zoneinfo(value: ZoneInfo) -> str:
    return str(value)
  1. This new function could be even generalized to accept multiple types, like
register_extra_hooks(IPv4Address, ZoneInfo)
  1. It is possible to support non-stdlib modules in this function, by e.g. checking __module__ string or using inspect.getmodule() before importing third-party module itself.

  2. Extra hooks could be registered by third-party libraries with e.g. pluggy.

Does anything of the mentioned above sound reasonable?

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reviewing the Converter hook-registration APIs and global_converter, then compare the proposed register_extra_hooks variants for stdlib types such as uuid, zoneinfo, ipaddress, and re.Pattern. Done means the scope and registration behavior are agreed, including whether multiple types and third-party hooks are supported; no test path is named in the issue.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
backend-api-design
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
30/100

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