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A lightweight library for converting complex datatypes into native Python datatypes.

Project description

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marshmallow is an ORM/ODM/framework-agnostic library for converting complex datatypes, such as objects, into native Python datatypes. The serialized objects can then be rendered to standard formats such as JSON for use in an HTTP API.

from datetime import datetime
from marshmallow import Serializer, fields, pprint

# A "model"
class Person(object):
    def __init__(self, name): = name
        self.date_born =

# A serializer
class PersonSerializer(Serializer):
    name = fields.String()
    date_born = fields.DateTime()

person = Person("Guido van Rossum")
serialized = PersonSerializer(person)
# {"name": "Guido van Rossum", "date_born": "Sun, 10 Nov 2013 14:24:50 -0000"}

Get It Now

$ pip install -U marshmallow


Full documentation is available at .


  • Python >= 2.6 or >= 3.3

marshmallow has no external dependencies outside of the Python standard library.


MIT licensed. See the bundled LICENSE file for more details.


0.7.0 (2014-06-22)

  • Add Serializer.error_handler decorator that registers a custom error handler.
  • Add Serializer.data_handler decorator that registers data post-processing callbacks.
  • Backwards-incompatible: process_data method is deprecated. Use the data_handler decorator instead.
  • Fix bug that raised error when passing extra data together with many=True. Thanks Joe Alcorn for reporting.
  • If required=True validation is violated for a given Field, it will raise an error message that is different from the message specified by the error argument. Thanks Anders Steinlein.
  • More generic error message raised when required field is missing.
  • validated decorator should only wrap a Field class’s output method.

0.6.0 (2014-06-03)

  • Fix bug in serializing keyed tuple types, e.g. namedtuple and KeyedTuple.
  • Nested field can load a serializer by its class name as a string. This makes it easier to implement 2-way nesting.
  • Make override-able.

0.5.5 (2014-05-02)

  • Add Serializer.factory for creating a factory function that returns a Serializer instance.
  • MarshallingError stores its underlying exception as an instance variable. This is useful for inspecting errors.
  • fields.Select is aliased to fields.Enum.
  • Add fields.__all__ and marshmallow.__all__ so that the modules can be more easily extended.
  • Expose Serializer.OPTIONS_CLASS as a class variable so that options defaults can be overridden.
  • Add Serializer.process_data hook that allows subclasses to manipulate the final output data.

0.5.4 (2014-04-17)

  • Add json_module class Meta option.
  • Add required option to fields . Thanks @DeaconDesperado.
  • Tested on Python 3.4 and PyPy.

0.5.3 (2014-03-02)

  • Fix Integer field default. It is now 0 instead of 0.0. Thanks @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.

0.5.2 (2014-02-10)

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

0.5.1 (2014-02-02)

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

0.5.0 (2013-12-29)

  • Can customize validation error messages by passing the error parameter to a field.
  • Backwards-incompatible: Rename fields.NumberField -> fields.Number.
  • Add fields.Select. Thanks @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.

0.4.1 (2013-12-01)

  • 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.

0.4.0 (2013-11-24)

  • Add additional clas Meta option.
  • Add dateformat class Meta option.
  • Support for serializing UUID, date, time, and timedelta objects.
  • Remove Serializer.to_data method. Just use property.
  • String field defaults to empty string instead of None.
  • Backwards-incompatible: isoformat and rfcformat functions moved to
  • Backwards-incompatible: Validation functions moved to
  • Backwards-incompatible: Remove
  • 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.

0.3.1 (2013-11-16)

  • 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.

0.3.0 (2013-11-14)

  • 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.

0.2.1 (2013-11-12)

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

0.2.0 (2013-11-11)

  • Field-level validation.
  • Add fields.Method.
  • Add fields.Function.
  • Allow binding of extra data to a serialized object by passing the extra param when initializing a Serializer.
  • Add relative paramater to fields.Url that allows for relative URLs.

0.1.0 (2013-11-10)

  • First release.

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