The CLI Tool

The wiz command provides a companion CLI tool for the Dataclass Wizard, which further simplifies interaction with the Python dataclasses module.

Getting help:

$ wiz -h
usage: wiz [-h] [-V] {gen-schema,gs} ...

A companion CLI tool for the Dataclass Wizard, which simplifies interaction with the Python `dataclasses` module.

positional arguments:
  {gen-schema,gs}  Supported sub-commands
    gen-schema (gs)
                   Generates a Python dataclass schema, given a JSON input.

optional arguments:
  -h, --help       show this help message and exit
  -V, --version    Display the version of this tool.

Checking the version of the CLI tool should display the currently installed version of the dataclass-wizard library:

$ wiz -V

To get help on a subcommand, simply use wiz <subcommand> -h. For example:

$ wiz gs -h

JSON To Dataclass Generation Tool

The subcommand gen-schema (aliased to gs) provides a JSON to Python schema generation tool. This utility takes a JSON file or string as an input, and outputs the corresponding dataclass schema. The main purpose is to easily create dataclasses that can be used with API output, without resorting to dict’s or NamedTuple’s.

This scheme generation tool is inspired by the following projects:


A few things to consider:

  • The script sometimes has to make some assumptions, so give the output a once-over.

  • In an array of objects (i.e. dictionaries), all key names and type definitions get merged into a single model dataclass, as the objects are considered homogenous in this case.

  • Deeply nested lists within objects (e.g. list -> dict -> list) should similarly merge all list elements with the other lists under that key in each sibling dict object.

  • The output is properly formatted, including additional spacing where needed. Please consider opening an issue if there are any potential improvements to be made.

Example usage:

echo '{
    "name": "Yavin IV",
    "rotation_period": "24",
    "orbital_period": "4818",
    "diameter": "10200",
    "climate": "temperate, tropical",
    "gravity": "1 standard",
    "terrain": "jungle, rainforests",
    "surface_water": "8",
    "population": "1000",
    "residents": [],
    "films": [
    "created": "2014-12-10T11:37:19.144000Z",
    "edited": "2014-12-20T20:58:18.421000Z",
    "url": ""
}' | wiz gs

Generates the following Python code:

from dataclasses import dataclass
from datetime import datetime
from typing import List, Union

class Data:
    Data dataclass

    name: str
    rotation_period: Union[int, str]
    orbital_period: Union[int, str]
    diameter: Union[int, str]
    climate: str
    gravity: str
    terrain: str
    surface_water: Union[int, str]
    population: Union[int, str]
    residents: List
    films: List[str]
    created: datetime
    edited: datetime
    url: str

Note: to write the output to a Python file instead of displaying the output in the terminal, pass the name of the output file. If the file has no extension, a default .py extension will be added.

For example:

# Note: the following command writes to a new file ''

echo '<json string>' | wiz gs - out

Future Annotations

Passing in the -x/--experimental flag will enable experimental features via a __future__ import, which allows PEP 585 and PEP 604- style annotations to be used in Python 3.7+

For example, assume your input.json file contains the following contents:

  "myField": null,
  "My_List": [],
  "Objects": [
      "key1": false
      "key1": 1.2,
      "key2": "string"
      "key1": "val",
      "key2": null

Then we could run the following command:

$ wiz gs -x input.json

The generated Python code is slightly different, as shown below. You might notice that a __future__ import is added at the top, for compatibility with versions earlier than Python 3.10. In the annotations, we also prefer to use parameterized standard collections, and use the new pipe | syntax to represent Union and Optional types.

from __future__ import annotations

from dataclasses import dataclass
from typing import Any

from dataclass_wizard import JSONWizard

class Data(JSONWizard):
    Data dataclass

    my_field: Any
    my_list: list
    objects: list[Object]

class Object:
    Object dataclass

    key1: bool | float | str
    key2: str | None