Marshmallow

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* 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.

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* 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.

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* 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.

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* Fix bug with serializing dictionaries.
* Fix error raised when serializing empty list.
* Add ``only`` and ``exclude`` parameters to Serializer constructor.
* Add ``strict`` parameter and option: causes Serializer to raise an error if invalid data are passed in, rather than storing errors.
* Updated Flask + SQLA example in docs.

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* Declaring Serializers just got easier. The ``class Meta`` paradigm allows you to specify fields more concisely. Can specify ``fields`` and ``exclude`` options.
* Allow date formats to be changed by passing ``format`` parameter to ``DateTime`` field constructor. Can either be ``"rfc"`` (default), ``"iso"``, or a date format string.
* More useful error message when declaring fields as classes (instead of an instance, which is the correct usage).
* Rename ``MarshallingException`` -> ``MarshallingError``.
* Rename ``marshmallow.core`` -> ``marshmallow.serializer``.

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* Allow prefixing field names.
* Fix storing errors on Nested Serializers.
* Python 2.6 support.