Marshmallow

++++++++++++++++++

* Fix ``Integer`` field default. It is now ``0`` instead of ``0.0``. Thanks :user:`kalasjocke`.
* Add ``context`` param to ``Serializer``. Allows accessing arbitrary objects in ``Function`` and ``Method`` fields.
* ``Function`` and ``Method`` fields raise ``MarshallingError`` if their argument is uncallable.

++++++++++++++++++

* Enable custom field validation via the ``validate`` parameter.
* Add ``utils.from_rfc`` for parsing RFC datestring to Python datetime object.

++++++++++++++++++

* Avoid unnecessary attribute access in ``utils.to_marshallable_type`` for improved performance.
* Fix RFC822 formatting for localized datetimes.

++++++++++++++++++

* Can customize validation error messages by passing the ``error`` parameter to a field.
* *Backwards-incompatible*: Rename ``fields.NumberField`` -> ``fields.Number``.
* Add ``fields.Select``. Thanks :user:`ecarreras`.
* Support nesting a Serializer within itself by passing ``"self"`` into ``fields.Nested`` (only up to depth=1).
* *Backwards-incompatible*: No implicit serializing of collections. Must set ``many=True`` if serializing to a list. This ensures that marshmallow handles singular objects correctly, even if they are iterable.
* If Nested field ``only`` parameter is a field name, only return a single value for the nested object (instead of a dict) or a flat list of values.
* Improved performance and stability.

++++++++++++++++++

* An object's ``__marshallable__`` method, if defined, takes precedence over ``__getitem__``.
* Generator expressions can be passed to a serializer.
* Better support for serializing list-like collections (e.g. ORM querysets).
* Other minor bugfixes.

++++++++++++++++++

* Add ``additional`` `class Meta` option.
* Add ``dateformat`` `class Meta` option.
* Support for serializing UUID, date, time, and timedelta objects.
* Remove ``Serializer.to_data`` method. Just use ``Serialize.data`` property.
* String field defaults to empty string instead of ``None``.
* *Backwards-incompatible*: ``isoformat`` and ``rfcformat`` functions moved to utils.py.
* *Backwards-incompatible*: Validation functions moved to validate.py.
* *Backwards-incompatible*: Remove types.py.
* Reorder parameters to ``DateTime`` field (first parameter is dateformat).
* Ensure that ``to_json`` returns bytestrings.
* Fix bug with including an object property in ``fields`` Meta option.
* Fix bug with passing ``None`` to a serializer.