Tin/override-metadata

HISTORY.md

@@ -4,10 +4,18 @@
 
 ## 24.1.0 (UNRELEASED)
 
+- Introduce {meth}`BaseConverter.get_structure_hook` and {meth}`BaseConverter.get_unstructure_hook` methods.
+  ([#432](https://github.com/python-attrs/cattrs/issues/432) [#472](https://github.com/python-attrs/cattrs/pull/472))
+- The default union handler now properly takes renamed fields into account.
+  ([#472](https://github.com/python-attrs/cattrs/pull/472))
 - Add support for [PEP 695](https://peps.python.org/pep-0695/) type aliases.
   ([#452](https://github.com/python-attrs/cattrs/pull/452))
+- The `include_subclasses` strategy now fetches the member hooks from the converter (making use of converter defaults) if overrides are not provided, instead of generating new hooks with no overrides.
+  ([#429](https://github.com/python-attrs/cattrs/issues/429) [#472](https://github.com/python-attrs/cattrs/pull/472))
 - The {class}`orjson preconf converter <cattrs.preconf.orjson.OrjsonConverter>` now passes through dates and datetimes to orjson while unstructuring, greatly improving speed.
   ([#463](https://github.com/python-attrs/cattrs/pull/463))
+- `cattrs.gen` generators now attach metadata to the generated functions, making them introspectable.
+  ([#472](https://github.com/python-attrs/cattrs/pull/472))
 - More robust support for `Annotated` and `NotRequired` in TypedDicts.
   ([#450](https://github.com/python-attrs/cattrs/pull/450))
 - `typing_extensions.Literal` is now automatically structured, just like `typing.Literal`.
@@ -16,6 +24,8 @@
   ([#452](https://github.com/python-attrs/cattrs/pull/452))
 - Imports are now sorted using Ruff.
 - Tests are run with the pytest-xdist plugin by default.
+- Rework the introductory parts of the documentation, introducing the Basics section.
+  ([#472](https://github.com/python-attrs/cattrs/pull/472))
 - The docs now use the Inter font.
 
 ## 23.2.3 (2023-11-30)

docs/basics.md

@@ -0,0 +1,112 @@
+# The Basics
+```{currentmodule} cattrs
+```
+
+All _cattrs_ functionality is exposed through a {class}`cattrs.Converter` object.
+A global converter is provided for convenience as {data}`cattrs.global_converter` but more complex customizations should be performed on private instances.
+
+
+## Converters
+
+The core functionality of a converter is [structuring](structuring.md) and [unstructuring](unstructuring.md) data by composing provided and [custom handling functions](customizing.md), called _hooks_.
+
+To create a private converter, instantiate a {class}`cattrs.Converter`. Converters are relatively cheap; users are encouraged to have as many as they need.
+
+The two main methods are {meth}`structure <cattrs.BaseConverter.structure>` and {meth}`unstructure <cattrs.BaseConverter.unstructure>`, these are used to convert between _structured_ and _unstructured_ data.
+
+```python
+>>> from cattrs import structure, unstructure
+>>> from attrs import define
+
+>>> @define
+... class Model:
+...    a: int
+
+>>> unstructure(Model(1))
+{"a": 1}
+>>> structure({"a": 1}, Model)
+Model(a=1)
+```
+
+_cattrs_ comes with a rich library of un/structuring rules by default, but it excels at composing custom rules with built-in ones.
+
+The simplest approach to customization is wrapping an existing hook with your own function.
+A base hook can be obtained from a converter and be subjected to the very rich mechanisms of Python function composition.
+
+```python
+>>> from cattrs import get_structure_hook
+
+>>> base_hook = get_structure_hook(Model)
+
+>>> def my_hook(value, type):
+...     # Apply any preprocessing to the value.
+...     result = base_hook(value, type)
+...     # Apply any postprocessing to the value.
+...     return result
+```
+
+This new hook can be used directly or registered to a converter (the original instance, or a different one).
+
+(`cattrs.structure({}, Model)` is shorthand for `cattrs.get_structure_hook(Model)({}, Model)`.)
+
+Another approach is to write a hook from scratch instead of wrapping an existing one.
+For example, we can write our own hook for the `int` class.
+
+```python
+>>> def my_int_hook(value, type):
+...     if not isinstance(value, int):
+...         raise ValueError('not an int!')
+...     return value
+```
+
+We can then register this hook to a converter, and any other hook converting an `int` will use it.
+Since this is an impactful change, we will switch to using a private converter.
+
+```python
+>>> from cattrs import Converter
+
+>>> c = Converter()
+
+>>> c.register_structure_hook(int, my_int_hook)
+```
+
+Now, if we ask our new converter for a `Model` hook, through the ✨magic of function composition✨ that hook will use our new `my_int_hook`.
+
+```python
+>>> base_hook = c.get_structure_hook(Model)
+>>> base_hook({"a": "1"}, Model)
+  + Exception Group Traceback (most recent call last):
+    |   File "...", line 22, in <module>
+    |     base_hook({"a": "1"}, Model)
+    |   File "<cattrs generated structure __main__.Model>", line 9, in structure_Model
+    | cattrs.errors.ClassValidationError: While structuring Model (1 sub-exception)
+    +-+---------------- 1 ----------------
+      | Traceback (most recent call last):
+      |   File "<cattrs generated structure __main__.Model>", line 5, in structure_Model
+      |   File "...", line 15, in my_int_hook
+      |     raise ValueError("not an int!")
+      | ValueError: not an int!
+      | Structuring class Model @ attribute a
+      +------------------------------------
+```
+
+To continue reading about customizing _cattrs_, see [](customizing.md).
+More advanced structuring customizations are commonly called [](strategies.md).
+
+## Global Converter
+
+Global _cattrs_ functions, such as {meth}`cattrs.unstructure`, use a single {data}`global converter <cattrs.global_converter>`.
+Changes done to this global converter, such as registering new structure and unstructure hooks, affect all code using the global functions.
+
+The following functions implicitly use this global converter:
+
+- {meth}`cattrs.structure`
+- {meth}`cattrs.unstructure`
+- {meth}`cattrs.get_structure_hook`
+- {meth}`cattrs.get_unstructure_hook`
+- {meth}`cattrs.structure_attrs_fromtuple`
+- {meth}`cattrs.structure_attrs_fromdict`
+
+Changes made to the global converter will affect the behavior of these functions.
+
+Larger applications are strongly encouraged to create and customize different, private instances of {class}`cattrs.Converter`.