jsonschema-gen is Python type hints parser which can convert function and method annotations into JSONSchema objects.

• Pythonic classes for JSONSchema types
• Extensive type coverage: TypedDict, Generic, NewType, etc.
• No external dependencies

With pip and python 3.8+:

pip3 install jsonschema-gen

See the user guide for more info.

Create a parser:

from jsonschema_gen import Parser

parser = Parser(strict=True)

Generate schema for your function or method from Python type hints (see the list of supported types):

from typing import NewType

UserName = NewType('UserName', str)

class UserData:
    def get_user(self, name: UserName, active: bool = True) -> dict:
        """Get user by username."""

annotation = parser.parse_function(UserData.get_user, UserData)

The result is an annotation object with input .kwargs and output .returns. You can get a JSONSchema compatible dict using json_repr() on .kwargs:

schema = annotation.kwargs.json_repr()

The result would look like this (if converted to JSON with dumps):

{
  "type": "object",
  "title": "Get user by username.",
  "properties": {
    "name": {
      "title": "Username",
      "type": "string"
    },
    "active": {
      "type": "boolean",
      "default": true
    }
  },
  "required": [
    "name"
  ],
  "additionalProperties": false
}

Use fastjsonschema or other JSONSchema validation library to create a validator for the schema:

from fastjsonschema import compile

validator = compile(schema)
valiator({'name': 'John', 'email': 'john@dowe'})

Alternatively you can pass the whole class to the parser to get the annotation mapping:

annotations = parser.parse_class(UserData)
annotations['get_user'].kwargs.json_repr()

The Python type hints are vast and yet not well organized, so there could always be some data type I forgot to add here. Read the customization guide to extend the standard list of type parsers.

Some annotations cannot be converted to JSONSchema objects, for example: positional-only arguments, variable positionals, etc. There are different strategies considering these types of parameters.

Python 3.8 compatibility is so-so due to lots of features and changes made in 3.9. However, it still should support most of the functionality.

Also read about the strict mode.