Marshmallow

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

Features:

- Add ``format`` option to ``Date`` field (:pr:`869`).
- *Backwards-incompatible*: Rename ``DateTime``'s ``dateformat`` Meta option
to ``datetimeformat``. ``dateformat`` now applies to ``Date`` (:pr:`869`).
Thanks :user:`knagra` for implementing these changes.
- Enforce ISO 8601 when deserializing date and time (:issue:`899`).
Thanks :user:`dushr` for the report and the work on the PR.
- *Backwards-incompatible*: Raise ``ValueError`` on ``Schema`` instantiation in
case of ``attribute`` or ``data_key`` collision (:pr:`992`).

Bug fixes:

- Fix inconsistencies in field inference by refactoring the inference feature
into a dedicated field (:issue:`809`). Thanks :user:`taion` for the PR.
- When ``unknown`` is not passed to ``Nested``, default to nested ``Schema``
``unknown`` meta option rather than ``RAISE`` (:pr:`963`).
Thanks :user:`vgavro` for the PR.
- Fix loading behavior of ``fields.Pluck`` (:pr:`990`).
- Includes bug fix from 2.16.0.

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

Bug fixes:

- Fix ``root`` attribute for nested container fields
on inheriting schemas (:issue:`956`). Thanks :user:`bmcbu`
for reporting.

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

Bug fixes:

- Raise ``ValidationError`` instead of ``TypeError`` when non-iterable types are
validated with ``many=True`` (:issue:`851`).
- ``many=True`` no longer iterates over ``str`` and ``collections.abc.Mapping`` objects and instead
raises a ``ValidationError`` with ``{'_schema': ['Invalid input type.']}`` (:issue:`930`).
- Return ``[]`` as ``ValidationError.valid_data`` instead of ``{}`` when
``many=True`` (:issue:`907`).

Thanks :user:`tuukkamustonen` for implementing these changes.

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

Features:

- Add ``fields.Pluck`` for serializing a single field from a nested object
(:issue:`800`). Thanks :user:`timc13` for the feedback and :user:`deckar01`
for the implementation.
- *Backwards-incompatible*: Passing a string argument as ``only`` to
``fields.Nested`` is no longer supported. Use ``fields.Pluck`` instead
(:issue:`800`).
- Raise a ``StringNotCollectionError`` if ``only`` or ``exclude`` is
passed as a string to ``fields.Nested`` (:pr:`931`).
- *Backwards-incompatible*: ``Float`` takes an ``allow_nan`` parameter to
explicitly allow serializing and deserializing special values (``nan``,
``inf`` and ``-inf``). ``allow_nan`` defaults to ``False``.

Other changes:

- *Backwards-incompatible*: ``Nested`` field now defaults to ``unknown=RAISE``
instead of ``EXCLUDE``. This harmonizes behavior with ``Schema`` that
already defaults to ``RAISE`` (:issue:`908`). Thanks :user:`tuukkamustonen`.
- Tested against Python 3.7.

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

Bug fixes:

- Errors reported by a schema-level validator for a field in a ``Nested`` field
are stored under corresponding field name, not ``_schema`` key (:pr:`862`).
- Includes bug fix from 2.15.4.

Other changes:

- *Backwards-incompatible*: The ``unknown`` option now defaults to ``RAISE``
(`524 (comment) <https://github.com/marshmallow-code/marshmallow/issues/524#issuecomment-397165731>`_,
:issue:`851`).
- *Backwards-incompatible*: When a schema error is raised with a ``dict`` as
payload, the ``dict`` overwrites any existing error list. Before this change,
it would be appended to the list.
- Raise a `StringNotCollectionError` if ``only`` or ``exclude`` is
passed as a string (:issue:`316`). Thanks :user:`paulocheque` for
reporting.

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

Features:

- The behavior to apply when encountering unknown fields while deserializing
can be controlled with the ``unknown`` option (:issue:`524`,
:issue:`747`, :issue:`127`).
It makes it possible to either "include", "exclude", or "raise".
Thanks :user:`tuukkamustonen` for the suggestion and thanks
:user:`ramnes` for the PR.

.. warning::

The default for ``unknown`` will be changed to ``RAISE`` in the
next release.

Other changes:

- *Backwards-incompatible*: Pre/Post-processors MUST return modified data.
Returning ``None`` does not imply data were mutated (:issue:`347`). Thanks
:user:`tdevelioglu` for reporting.
- *Backwards-incompatible*: ``only`` and ``exclude`` are bound by
declared and additional fields. A ``ValueError`` is raised if invalid
fields are passed (:issue:`636`). Thanks :user:`jan-23` for reporting.
Thanks :user:`ikilledthecat` and :user:`deckar01` for the PRs.
- Format code using pre-commit (:pr:`855`).

Deprecations/Removals:

- ``ValidationError.fields`` is removed (:issue:`840`). Access field
instances from ``Schema.fields``.