Wizard Mixin Classes

In addition to the JSONWizard, here a few extra Wizard Mixin classes that might prove to be quite convenient to use.

JSONListWizard

The JSON List Wizard is a Mixin class that extends JSONWizard to return Container - instead of list - objects.

Note

Container objects are simply convenience wrappers around a collection of dataclass instances. For all intents and purposes, they behave exactly the same as list objects, with some added helper methods:

• prettify() - Convert the list of instances to a prettified JSON string.

• to_json() - Convert the list of instances to a JSON string.

• to_json_file() - Serialize the list of instances and write it to a JSON file.

Simple example of usage below:

from __future__ import annotations  # Note: In 3.10+, this import can be removed

from dataclasses import dataclass

from dataclass_wizard import JSONListWizard, Container


@dataclass
class Outer(JSONListWizard):
    my_str: str | None
    inner: list[Inner]


@dataclass
class Inner:
    other_str: str


my_list = [
    {"my_str": 20,
     "inner": [{"otherStr": "testing 123"}]},
    {"my_str": "hello",
     "inner": [{"otherStr": "world"}]},
]

# De-serialize the JSON string into a list of `MyClass` objects
c = Outer.from_list(my_list)

# Container is just a sub-class of list
assert isinstance(c, list)
assert type(c) == Container

print(c)
# [Outer(my_str='20', inner=[Inner(other_str='testing 123')]),
#  Outer(my_str='hello', inner=[Inner(other_str='world')])]

print(c.prettify())
# [
#   {
#     "myStr": "20",
#   ...

# serializes the list of dataclass instances to a JSON file
c.to_json_file('my_file.json')

JSONFileWizard

The JSON File Wizard is a minimalist Mixin class that makes it easier to interact with JSON files, as shown below.

It comes with only two added methods: from_json_file() and to_json_file().

Note

This can be paired with the JSONWizard Mixin class for more complete extensibility.

from __future__ import annotations  # Note: In 3.10+, this import can be removed

from dataclasses import dataclass

from dataclass_wizard import JSONFileWizard


@dataclass
class MyClass(JSONFileWizard):
    my_str: str | None
    my_int: int = 14


c1 = MyClass(my_str='Hello, world!')
print(c1)

# Serializes the dataclass instance to a JSON file
c1.to_json_file('my_file.json')

# contents of my_file.json:
#> {"myStr": "Hello, world!", "myInt": 14}

c2 = MyClass.from_json_file('my_file.json')

# assert that data is the same
assert c1 == c2

YAMLWizard

The YAML Wizard leverages the PyYAML library – which can be installed as an extra via pip install dataclass-wizard[yaml] – to easily convert dataclass instances to/from YAML.

Note

The default key transform used in the YAML dump process is lisp-case, however this can easily be customized without the need to sub-class from JSONWizard, as shown below.

>>> @dataclass
>>> class MyClass(YAMLWizard, key_transform='CAMEL'):
>>>     ...

A (mostly) complete example of using the YAMLWizard is as follows:

from __future__ import annotations  # Note: In 3.10+, this import can be removed

from dataclasses import dataclass, field

from dataclass_wizard import YAMLWizard


@dataclass
class MyClass(YAMLWizard):
    str_or_num: str | int = 42
    nested: MyNestedClass | None = None


@dataclass
class MyNestedClass:
    list_of_map: list[dict[int, str]] = field(default_factory=list)
    my_int: int = 14


c1 = MyClass.from_yaml("""
str-or-num: 23
nested:
    ListOfMap:
        - 111: Hello,
          222: World!
        - 333: 'Testing'
          444: 123
""")

# serialize the dataclass instance to a YAML file
c1.to_yaml_file('my_file.yaml')

# sample contents of `my_file.yaml` would be:
#> nested:
#>   list-of-map:
#>   - 111: Hello,
#>   ...

# now read it back...
c2 = MyClass.from_yaml_file('my_file.yaml')

# assert we get back the same data
assert c1 == c2

# let's create a list of dataclass instances
objects = [MyClass(), c2, MyClass(3, nested=MyNestedClass())]

# and now, serialize them all...
yaml_string = MyClass.list_to_yaml(objects)

print(yaml_string)
# - nested: null
#   str-or-num: 42
# - nested:
#     list-of-map:
#   ...