0.22.2 (2022-10-11)

Features and Improvements

  • Minor performance improvement when dumping custom sub-types or unhandled types, such that we cache the dump hook for the type so that subsequent lookups are faster overall.

0.22.1 (2022-05-11)

Features and Improvements

  • Update MissingFields to provide a more user-friendly error message, in cases where a missing dataclass field is not snake-cased, but could - with the right key transform - map to a key in the JSON object. For example, a JSON key of myField and a field named MyField.


  • Fixed a bug in the load (or de-serialization) process with from_dict, where a MissingFields was raised in cases where a dataclass field is not snake-cased, but is otherwise identical to a key in the JSON object. For example, a JSON key and field both named viewMode. The JSON data in such cases should now be correctly de-serialized to a dataclass instance as expected.

0.22.0 (2022-02-02)

Features and Improvements

  • Ensure that the debug_enabled flag now applies recursively to all nested dataclasses, which is more helpful for debugging purposes.

  • Add new attribute json_object – which contains the original JSON object – to ParseError objects, and include it in the object representation.


  • Fixed an issue with the debug_enabled flag enabled, where some load hooks were not properly decorated when debug mode was enabled; errors were not properly formatted in these cases. To elaborate, this only affected load hooks decorated with a @_single_arg_alias. In particular, this affected the load hooks for a few annotated types, such as float and enum.

0.21.0 (2022-01-23)

Features and Improvements

  • Adds few extra Wizard Mixin classes that might prove incredibly convenient to use.

    • JSONListWizard - Extends JSONWizard to return Container – instead of list – objects where possible.

    • JSONFileWizard - Makes it easier to convert dataclass instances from/to JSON files on a local drive.

    • YAMLWizard - Provides support to convert dataclass instances to/from YAML, using the default PyYAML parser.

  • Add a new Container model class, a list sub-type which acts as a convenience wrapper around a collection of dataclass instances.

  • The dataclass-wizard library now supports parsing of YAML data. It adds the PyYAML as an optional dependency, which is loaded when it’s used for the initial time. This extra dependency can be installed via:

    $ pip install dataclass-wizard[yaml]

0.20.3 (2021-11-30)

  • Update the parsing logic in as_timedelta() for timedelta annotated types so we now explicitly check the types. If the value is numeric, or if it’s a string in a numeric value like “1.2”, we can parse it directly and so avoid calling the pytimeparse module.

0.20.1 - 0.20.2 (2021-11-27)

  • Update and refactor docs, doc layout, and the readme.

  • Move benchmark tests to the benchmarks/ directory.

0.20.0 (2021-11-23)

  • Support custom patterns for dates and times, which are parsed (de-serialized) using datetime.strptime(). This allows two approaches to be used, which have complete support in Python 3.7+ currently:

    • Using the DatePattern, TimePattern, and DateTimePattern type annotations, representing patterned date, time, and datetime objects respectively.

    • Use Annotated to annotate the field as list[time] for example, and pass in Pattern() as an extra.

0.19.0 (2021-11-17)

Features and Improvements

  • Add the option to customize the name of the tag key that will be used to (de)serialize fields that contain dataclasses within Union types. A new attribute tag_key in the Meta config determines the key in the JSON object that will be used for this purpose, which defaults to __tag__ if not specified.

  • Add the ability to auto-generate tags for a class - using the name of the class - if a value for tag is not specified in the Meta config for a dataclass that appears within a Union declaration. A new flag auto_assign_tags in the Meta config can be enabled to allow auto-assigning the class name as a tag.

0.18.0 (2021-11-14)

Breaking Changes

  • The LoadMeta() and DumpMeta() helper functions no longer accept a class type as the first argument; the correct usage now is to invoke the bind_to() method on the Meta config returned. That is, given a dataclass A, replace the following syntax:

    LoadMeta(A, **kwargs)

    with a more explicit binding:

  • The asdict() helper function no longer accepts a Meta config as an argument. This is to encourage the usage of LoadMeta() and DumpMeta(), as mentioned above. The main impetus for this change is performance, since the Meta config for a class only needs to be set up once using this approach.

  • Updated the project status from Beta to Production/Stable, to signify that any further breaking changes will result in bumping the major version.

Features and Improvements

  • Add the bind_to() method to the base Meta class, BaseJSONWizardMeta.

  • Meta config specified for a main dataclass (i.e. the class passed in to from_dict and to_dict) now applies recursively to any nested dataclasses by default. The Meta config from the main class will be merged with the Meta config for each nested class. Note that this behavior can be disabled however, with the recursive parameter passed in to the Meta config.

  • Rename BaseMeta to AbstractMeta, as the name should be overall more clearer, since it’s actually an abstract class.

0.17.1 (2021-11-04)

  • property_wizard: Update the metaclass to support new-style annotations, also via a __future__ import declared at a the top of a module; this allows PEP 585 and PEP 604 style annotations to be used in Python 3.7 and higher.

0.17.0 (2021-10-28)

  • Support new-style annotations in Python 3.7+, via a __future__ import declared at a the top of a module; this allows PEP 585 and PEP 604 style annotations to be used in Python 3.7 and higher.

  • wiz CLI: Add the -x / –experimental flag, which instead uses new-style annotations in the generated Python code.

  • Update the docs and readme with examples and usage of future annotations in Python 3.7+.

0.16.2 (2021-10-26)

  • Minor code refactor and cleanup to support ForwardRef in Python 3.6 a little better.

0.16.1 (2021-10-21)

  • Add full support for Python 3.10

0.16.0 (2021-10-20)

  • Add support for serializing datetime.timedelta

    • Requires an extra for de-serialization, can be installed via pip install dataclass-wizard[timedelta].

0.15.2 (2021-10-03)

Features and Improvements

  • Add new internal helper function eval_forward_ref_if_needed()


  • Support forward references in type arguments to Union, as well as when iterating over the list of dataclasses.fields() for each data class.

0.15.1 (2021-09-30)

  • Add a new method list_to_json() to the JSONWizard Mixin class, which can be used to convert a list of dataclass instances to a JSON string representation.

  • Minor code refactoring to introduce small typing-related changes.

  • Update docs.

0.15.0 (2021-09-30)

  • Add the ability to skip fields with default values in the serialization process. A new attribute skip_defaults in the inner Meta class determines whether to skip / omit fields with default values, based on the default or default_factory argument to dataclasses.field().

  • Add the ability to omit fields in the serialization process.

    • A new argument dump added to the json_key() and json_field() helper functions determines whether to exclude the field in the JSON or dictionary result.

    • The asdict() helper function has similarly been updated to accept a exclude argument, containing a list of one or more dataclass field names to exclude from the serialization process.

0.14.2 (2021-09-28)


  • Dataclass fields that are excluded from the constructor method - i.e. ones defined like field(init=False...) - should now be similarly handled in the de-serialization process.

0.14.1 (2021-09-26)


  • The Meta.tag field should be updated to a ClassVar to help reduce the memory footprint.

0.14.0 (2021-09-25)

Features and Improvements

  • Add the ability to handle de-serialization and serialization of dataclasses within Union types. A new attribute tag in the inner Meta class determines the tag name to map to a dataclass, when the dataclass is part of any Union types.

  • The dump (serialization) process has been reworked to function more like the load process. That is, it will properly use the Meta config for a dataclass, as well as any custom load hooks for nested dataclasses. Performance or functionality should not otherwise be affected.

0.13.1 (2021-09-24)


  • Ensure that setup_dump_config_for_cls_if_needed() is called for nested dataclasses, so that custom key mappings for example can be properly applied.

0.13.0 (2021-09-08)

Features and Improvements

  • Add new error class MissingData, which is raised when a dataclass field annotated as a data class type has a null JSON value in the load process.

  • Update the as_int() helper function so that float values as well as ones encoded as strings are correctly converted to annotated int types, i.e. using the int(round(float)) syntax.

  • Add Encoder and Decoder model classes, and properly implement them in the JSONWizard helper methods.

  • Decorate the JSONWizard helper methods from_list(), from_dict(), and to_dict() with the _alias decorator.


  • property_wizard: Remove the internal usage of get_type_hints_with_extras() for resolving class annotations. This is because typing.get_type_hints will raise an error if a class has forward references in any type annotations. Since the usage is as a metaclass, forward refs can never be resolved. So we will instead access the class __annotations directly, and for now will ignore any forward references which are declared.

  • Ensure fromlist() is actually exported at the top level (looks like that was not the case)

0.12.0 (2021-09-06)

  • Change the order of arguments for fromdict() and fromlist() functions, since it’s more intuitive to pass the name of the data class as the first argument.

  • Add fromlist(), fromdict(), and asdict() to the public API, and ensure that we export these helper functions.

  • Add new helper functions LoadMeta() and DumpMeta() to specify the meta config for a dataclass, which can be used with the new functions like fromdict above.

  • Custom key mappings: support a use case where we want to specify a new mapping via the __remapping__ key in the metadata argument to dataclasses.field().

0.11.0 (2021-09-04)

  • Add the ability to handle unknown or extraneous JSON keys in the load (de-serialization) process. A new attribute raise_on_unknown_json_key to the Meta class determines if we should raise an error in such cases.

  • Move attribute definition for the JSONWizard.Meta class into a new BaseMeta definition, so that the model can be re-used in loaders and dumpers module for example.

  • Ensure all errors raised by this library extend from a new base error class, JSONWizardError.

  • Add new error classes

    • MissingFields - raised when JSON object is missing a required dataclass field.

    • UnknownJSONKey - raised when an unknown or extraneous JSON key is encountered in the JSON load process.

  • Split up the load (de-serialization) process for named tuples into two helper load hooks. The new hook load_to_named_tuple_untyped() is used for the collections.namedtuple variant.

  • Minor performance improvements so the JSON load process is slightly faster.

0.10.2 (2021-08-29)

  • Rename some internal functions, such as the default_func decorator (renamed to _alias). I felt that this name was overall more clearer.

  • Similarly rename PassThroughParser to SingleArgParser, as that’s a bit more clear which types it handles.

  • wiz CLI: comment out the –verbose and –quiet flags, as those were unused anyway.

  • Update docs/

0.10.0 (2021-08-28)

  • Minor performance improvements so the JSON load process is slightly faster.

  • wiz gs: The result now includes the JSONWizard import and the expected usage by default.

  • Update type annotations slightly for the LoadMixin.load_to... methods.

  • Add support for sub-classes of common Python types, such as subclasses of str and int, as part of the JSON load process.

  • Remove ForwardRefParser - we don’t need it anyway as it’s a simple resolution, and the usage of a Parser object incurs a bit of an unnecessary overhead.

0.9.0 (2021-08-23)

Features and Improvements

  • Minor performance improvements so the JSON load process is slightly faster.

  • Replace CaseInsensitiveDict with a custom DictWithLowerStore implementation.

  • wiz CLI: Add a --version option to check the installed version.

  • Remove get_class_name() usage wherever possible.


  • Fixes for the JSON to dataclass generation tool
    • Ensure that nested lists with dictionaries are correctly merged, and add a test case to confirm intended behavior.

    • Change to only singularize model names if nested within a list.

0.8.2 (2021-08-22)


  • wiz gs: Empty lists should appear as List instead of Dict

0.8.1 (2021-08-22)


  • Fix an import issue with the wiz CLI tool.

0.8.0 (2021-08-22)

Features and Improvements

  • Add new wiz companion CLI utility

  • Add a CLI sub-command gs to generate the dataclass schema for a JSON file or string input.


  • The key transform functions now correctly work when the JSON keys contain spaces. For example, a field named “the number 42” should now be correctly parsed as the_number_42 when the key transformer is to_snake_case().

0.7.0 (2021-08-19)

  • Support the deque type in the JSON load and dump process, as well as its equivalent in the typing module.

  • Add __slots__ where possible to classes, to help reduce the overall memory footprint.

  • Slightly changed the order of constructor arguments to most Parser implementations.

  • Rename the type_check utils module to typing_compat, as I think this name makes it clearer as to its purpose.

  • Rename a few internal functions, such as BaseJSONWizardMeta._safe_as_enum -> BaseJSONWizardMeta._as_enum_safe

  • Add benchmark tests against a few other libraries

0.6.0 (2021-08-16)

  • Support set and frozenset types in the JSON load and dump process, as well as their equivalents in the typing module.

  • Support custom JSON key mappings for dataclass fields.

  • Add new exported helper functions:
    • json_field: This can be thought of as an alias to dataclasses.field(...), but one which also represents a mapping of one or more JSON key names to a dataclass field.

    • json_key: Represents a mapping of one or more JSON key names for a dataclass field.

  • Add an optional attribute json_key_to_field to JSONSerializable.Meta

  • Rename ListParser to IterableParser, since this parser will also be used for Set types.

  • Update the __call__ method of the default Parser to raise a ParseError, so we can provide a more helpful error message when an unknown or unsupported type annotation is encountered.

0.5.1 (2021-08-13)


  • The property_wizard metaclass should now correctly handle cases when field properties are annotated as a standard mutable type (list, dict, or set).

  • The property_wizard metaclass should now also honor the default_factory argument to a dataclass field object as expected.

  • Resolved an issue where in some cases the JSON load/dump process failed when Python 3.8+ users imported TypedDict from typing instead of the typing_extensions module. Now it should correctly work regardless of which version of TypedDict is used. This is especially important because of an issue with TypedDict that is present in Python 3.8.

0.5.0 (2021-08-12)

Features and Improvements

  • JSONSerializable now supports dataclass fields with an Annotated type.

  • The property_wizard metaclass has been (similarly) updated to support Annotated field properties; such types can be resolved by making a call to typing.get_type_hints with the argument include_extras=True.

  • Support for adding global JSON load/dump settings, e.g. when JSONSerializable.Meta is defined as an outer class.

  • Add proper source attributions, and apply the LICENSE and any NOTICE (if applicable) from the sources.

  • Update comments in code to clarify or elaborate where needed.

  • Update Sphinx docs/


  • When JSONSerializable.Meta is defined as an inner class - which is the most common scenario - it should now be correctly applied per-class, rather than mutating the load/dump process for other dataclasses that don’t define their own inner Meta class.

  • When logging a message if a JSON key is missing from a dataclass schema, the dataclass name is now also included in the message.

0.4.1 (2021-08-09)

  • Update README docs with usage of newly supported features

0.4.0 (2021-08-09)

Features and Improvements

  • Add support for serializing the following Python types:
    • defaultdict (via the typing.DefaultDict annotation)

    • UUID’s

    • The special variadic form of Tuple. For example, Tuple[str, ...].

    • A special case where optional type arguments are passed to Tuple. For example, Tuple[str, Optional[int], Union[bool, str, None]]

  • Add new LetterCase.LISP Enum member, which references the to_lisp_case helper function

  • All the Enum-subclass attributes in JSONSerializable.Meta now additionally support strings as values; they will be parsed using the Enum name field by default, and should format helpful messages on any lookup errors.

  • Remove the LoadMixin.load_with_object method, as that was already deprecated and slated to be removed.


  • Update the get_class_name helper function to handle the edge case when classes are defined within a function.

  • Update a few load_to... methods as a staticmethod

0.3.0 (2021-08-05)

  • Some minor code refactoring

  • Require typing-extensions library up till Python 3.9 now (it’s main use for Python 3.8 and 3.9 is the updated get_origin and get_args helper functions)

  • The default __str__ method is now optional, and can be skipped via the flag str=False

  • Add some more test cases

0.2.4 (2021-08-04)

  • Update README docs

    • Move the section on Advanced Usage to the main docs

    • Cleanup usage and docs in the Field Properties section

0.2.3 (2021-08-03)

  • Add better keywords for the package

0.2.2 (2021-08-03)

  • Explicitly add a dependency on typing-extensions for Python 3.6 and 3.7

0.2.1 (2021-08-03)

  • Fix a bug for Python 3.6 where the build failed when using the PyForwardRef annotation.

0.2.0 (2021-08-03)

  • Rename type variable EXPLICIT_NULL to ExplicitNull

  • Rename module type_defs.py to type_def.py

  • Rename module base_meta.py to bases_meta.py

  • JSONSerializable.Meta: rename attribute date_time_with_dump to marshal_date_time_as, as I believe this name is overall more clearer.

  • Refactor the property_wizard helper function and update it to cover some edges cases.

  • Add test cases to confirm intended functionality of property_wizard.

0.1.0 (2021-08-02)

  • First release on PyPI.