Marshmallow

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Bug fixes:

- Fix serialization of collections for which ``iter`` will modify position, e.g. Pymongo cursors (:issue:`303`). Thanks :user:`Mise` for the catch and patch.

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Bug fixes:

- Fix passing data to schema validator when using ``validates_schema(many=True)`` (:issue:`297`). Thanks :user:`d-sutherland` for reporting.
- Fix usage of ``validates`` with a nested field when ``many=True`` (:issue:`298`). Thanks :user:`nelfin` for the catch and patch.

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Bug fixes:

- ``Constant`` field deserializes to its value regardless of whether its field name is present in input data (:issue:`291`). Thanks :user:`fayazkhan` for reporting.

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Features:

- Add ``Dict`` field for arbitrary mapping data (:issue:`251`). Thanks :user:`dwieeb` for adding this and :user:`Dowwie` for the suggestion.
- Add ``Field.root`` property, which references the field's Schema.

Deprecation/Removals:

- The ``extra`` param of ``Schema`` is deprecated. Add extra data in a ``post_load`` method instead.
- ``UnmarshallingError`` and ``MarshallingError`` are removed.

Bug fixes:

- Fix storing multiple schema-level validation errors (:issue:`287`). Thanks :user:`evgeny-sureev` for the patch.
- If ``missing=None`` on a field, ``allow_none`` will be set to ``True``.

Other changes:

- A ``List's`` inner field will have the list field set as its parent. Use ``root`` to access the ``Schema``.

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Features:

- Make error messages configurable at the class level and instance level (``Field.default_error_messages`` attribute and ``error_messages`` parameter, respectively).

Deprecation/Removals:

- Remove ``make_object``. Use a ``post_load`` method instead (:issue:`277`).
- Remove the ``error`` parameter and attribute of ``Field``.
- Passing string arguments to ``required`` and ``allow_none`` is deprecated. Pass the ``error_messages`` argument instead. **This API will be removed in version 2.2**.
- Remove ``Arbitrary``, ``Fixed``, and ``Price`` fields (:issue:`86`). Use ``Decimal`` instead.
- Remove ``Select`` / ``Enum`` fields (:issue:`135`). Use the ``OneOf`` validator instead.

Bug fixes:

- Fix error format for ``Nested`` fields when ``many=True``. Thanks :user:`alexmorken`.
- ``pre_dump`` methods are invoked before implicit field creation. Thanks :user:`makmanalp` for reporting.
- Return correct "required" error message for ``Nested`` field.
- The ``only`` argument passed to a ``Schema`` is bounded by the ``fields`` option (:issue:`183`). Thanks :user:`lustdante` for the suggestion.

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Deprecation/Removals:

- ``make_object`` is deprecated. Use a ``post_load`` method instead (:issue:`277`). **This method will be removed in the final 2.0 release**.
- ``Schema.accessor`` and ``Schema.error_handler`` decorators are deprecated. Define the ``accessor`` and ``error_handler`` class Meta options instead.

Bug fixes:

- Allow non-field names to be passed to ``ValidationError`` (:issue:`273`). Thanks :user:`evgeny-sureev` for the catch and patch.