JSON Schema-powered type annotations

This package provides a way to automatically produce type annotations based on jsonschema-schemas.

Not all concepts covered by jsonschema are expressible within Python typing annotations. However, most things will work like you'd expect. Most types are translated trivially (integer, number, string, array, boolean and null). The interesting type is object, which is translated into a TypedDict.

Warning: This is based on the mypy plugin system, which is stated to have no backwards compatibility guarantee. New versions of mypy might not be supported immediately.

Example

A JSON schema:

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "$id": "http://foo.qwerty/some/schema#",
    "title": "Foo Schema",
    "type": "object",
    "properties": {
        "title": {
            "type": "string"
        },
        "awesome": {
            "type": "number"
        }
    },
    "required": ["title"]
}

A TypedDict:

from typing import TYPE_CHECKING
from jsonschema_typed import JSONSchema

data: JSONSchema["path/to/schema.json"] = {"title": "baz"}

if TYPE_CHECKING:
    reveal_type(data)  # Revealed type is 'TypedDict('FooSchema', {'title': builtins.str,
                       #                                           'awesome'?: Union[builtins.int, builtins.float]})'
data["description"] = "there is no description"  # TypedDict "FooSchema" has no key 'description'
data["awesome"] = 42
data["awesome"] = None  # Argument 2 has incompatible type "None"; expected "Union[int, float]"

You can also get types of parts of a schema, as well as types of elements in arrays. Take a look at the test cases for more examples of usage.

Installation

pip install jsonschema-typed

You also need to enable the plugin(s) in your mypy.ini configuration file:

# mypy.ini
[mypy]
plugins = jsonschema_typed.plugin, jsonschema_typed.optional_typed_dict

# Due to a quirk of how these type hints are generated, mypy's caching breaks.
# Disabling caching might be required.
cache_dir = /dev/null

Requirements

The above installations resolves the dependencies, which consist of mypy and jsonschema (naturally). Testing has been done with versions:

• mypy==0.761
• jsonschema==3.2.0

Probably some older versions will also work. Report an issue if you need other versions.

Limitations

• additionalProperties doesn't really have an equivalent in TypedDict.
• The default keyword is not supported; but see: https://github.com/python/mypy/issues/6131.
• Self-references (e.g. "#") can't really work properly until nested forward-references are supported; see: https://github.com/python/mypy/issues/731.