Marshmallow

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Bug fixes:

- A ``Schema's`` ``error_handler``--if defined--will execute if ``Schema.validate`` returns validation errors (:issue:`121`).
- Deserializing `None` returns `None` rather than raising an ``AttributeError`` (:issue:`123`). Thanks :user:`RealSalmon` for the catch and patch.

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Features:

- Add ``QuerySelect`` and ``QuerySelectList`` fields (:issue:`84`).
- Convert validators in ``marshmallow.validate`` into class-based callables to make them easier to use when declaring fields (:issue:`85`).
- Add ``Decimal`` field which is safe to use when dealing with precise numbers (:issue:`86`).

Thanks :user:`philtay` for these contributions.

Bug fixes:

- ``Date`` fields correctly deserializes to a ``datetime.date`` object when ``python-dateutil`` is not installed (:issue:`79`). Thanks :user:`malexer` for the catch and patch.
- Fix bug that raised an ``AttributeError`` when using a class-based validator.
- Fix ``as_string`` behavior of Number fields when serializing to default value.
- Deserializing ``None`` or the empty string with either a ``DateTime``, ``Date``, ``Time`` or ``TimeDelta`` results in the correct unmarshalling errors (:issue:`96`). Thanks :user:`svenstaro` for reporting and helping with this.
- Fix error handling when deserializing invalid UUIDs (:issue:`106`). Thanks :user:`vesauimonen` for the catch and patch.
- ``Schema.loads`` correctly defaults to use the value of ``self.many`` rather than defaulting to ``False`` (:issue:`108`). Thanks :user:`davidism` for the catch and patch.
- Validators, data handlers, and preprocessors are no longer shared between schema subclasses (:issue:`88`). Thanks :user:`amikholap` for reporting.
- Fix error handling when passing a ``dict`` or ``list`` to a ``ValidationError`` (:issue:`110`). Thanks :user:`ksesong` for reporting.

Deprecation:

- The validator functions in the ``validate`` module are deprecated in favor of the class-based validators (:issue:`85`).
- The ``Arbitrary``, ``Price``, and ``Fixed`` fields are deprecated in favor of the ``Decimal`` field (:issue:`86`).

Support:

- Update docs theme.
- Update contributing docs (:issue:`77`).
- Fix namespacing example in "Extending Schema" docs. Thanks :user:`Ch00k`.
- Exclude virtualenv directories from syntax checking (:issue:`99`). Thanks :user:`svenstaro`.

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Features:

- Add ``Schema.validate`` method which validates input data against a schema. Similar to ``Schema.load``, but does not call ``make_object`` and only returns the errors dictionary.
- Add several validation functions to the ``validate`` module. Thanks :user:`philtay`.
- Store field name and instance on exceptions raised in ``strict`` mode.

Bug fixes:

- Fix serializing dictionaries when field names are methods of ``dict`` (e.g. ``"items"``). Thanks :user:`rozenm` for reporting.
- If a Nested field is passed ``many=True``, ``None`` serializes to an empty list. Thanks :user:`nickretallack` for reporting.
- Fix behavior of ``many`` argument passed to ``dump`` and ``load``. Thanks :user:`svenstaro` for reporting and helping with this.
- Fix ``skip_missing`` behavior for ``String`` and ``List`` fields. Thanks :user:`malexer` for reporting.
- Fix compatibility with python-dateutil 2.3.
- More consistent error messages across ``DateTime``, ``TimeDelta``, ``Date``, and ``Time`` fields.

Support:

- Update Flask and Peewee examples.

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Hotfix release.

- Ensure that errors dictionary is correctly cleared on each call to ``Schema.dump`` and ``Schema.load``.

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Adds new features, speed improvements, better error handling, and updated documentation.

- Add ``skip_missing`` ``class Meta`` option.
- A field's ``default`` may be a callable.
- Allow accessor function to be configured via the ``Schema.accessor`` decorator or the ``__accessor__`` class member.
- ``URL`` and ``Email`` fields are validated upon serialization.
- ``dump`` and ``load`` can receive the ``many`` argument.
- Move a number of utility functions from fields.py to utils.py.
- More useful ``repr`` for ``Field`` classes.
- If a field's default is ``fields.missing`` and its serialized value is ``None``, it will not be included in the final serialized result.
- Schema.dumps no longer coerces its result to a binary string on Python 3.
- *Backwards-incompatible*: Schema output is no longer an ``OrderedDict`` by default. If you want ordered field output, you must explicitly set the ``ordered`` option to ``True``.
- *Backwards-incompatible*: ``error`` parameter of the ``Field`` constructor is deprecated. Raise a ``ValidationError`` instead.
- Expanded test coverage.
- Updated docs.

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Major reworking and simplification of the public API, centered around support for deserialization, improved validation, and a less stateful ``Schema`` class.

* Rename ``Serializer`` to ``Schema``.
* Support for deserialization.
* Use the ``Schema.dump`` and ``Schema.load`` methods for serializing and deserializing, respectively.
* *Backwards-incompatible*: Remove ``Serializer.json`` and ``Serializer.to_json``. Use ``Schema.dumps`` instead.
* Reworked fields interface.
* *Backwards-incompatible*: ``Field`` classes implement ``_serialize`` and ``_deserialize`` methods. ``serialize`` and ``deserialize`` comprise the public API for a ``Field``. ``Field.format`` and ``Field.output`` have been removed.
* Add ``exceptions.ForcedError`` which allows errors to be raised during serialization (instead of storing errors in the ``errors`` dict).
* *Backwards-incompatible*: ``DateTime`` field serializes to ISO8601 format by default (instead of RFC822).
* *Backwards-incompatible*: Remove ``Serializer.factory`` method. It is no longer necessary with the ``dump`` method.
* *Backwards-incompatible*: Allow nesting a serializer within itself recursively. Use ``exclude`` or ``only`` to prevent infinite recursion.
* *Backwards-incompatible*: Multiple errors can be stored for a single field. The errors dictionary returned by ``load`` and ``dump`` have lists of error messages keyed by field name.
* Remove ``validated`` decorator. Validation occurs within ``Field`` methods.
* ``Function`` field raises a ``ValueError`` if an uncallable object is passed to its constructor.
* ``Nested`` fields inherit context from their parent.
* Add ``Schema.preprocessor`` and ``Schema.validator`` decorators for registering preprocessing and schema-level validation functions respectively.
* Custom error messages can be specified by raising a ``ValidationError`` within a validation function.
* Extra keyword arguments passed to a Field are stored as metadata.
* Fix ordering of field output.
* Fix behavior of the ``required`` parameter on ``Nested`` fields.
* Fix serializing keyed tuple types (e.g. ``namedtuple``) with ``class Meta`` options.
* Fix default value for ``Fixed`` and ``Price`` fields.
* Fix serialization of binary strings.
* ``Schemas`` can inherit fields from non-``Schema`` base classes (e.g. mixins). Also, fields are inherited according to the MRO (rather than recursing over base classes). Thanks :user:`jmcarp`.
* Add ``Str``, ``Bool``, and ``Int`` field class aliases.