pyvial 0.4.0

A micro web framework for AWS Lambda.

Vial

A micro web framework for AWS Lambda.

Installation

To add vial to your project, run the following command:

pip install pyvial

Usage

Entry Point

The main entry point of the application is always the Vial#__call__ function. When deploying to AWS Lambda, the Lambda handler should point to the Vial object in whichever file it's defined in. As an example:

from vial.app import Vial

app = Vial()

If this code snippet is defined in an app.py file, the handler would be app.app.

Basic API

from typing import Mapping
from vial.app import Vial

app = Vial()


@app.get("/hello-world")
def hello_world() -> Mapping[str, str]:
    return {"hello": "world"}

Path Parameters

You can define path parameters like this:

@app.get("/users/{user_id}")
def get_user(user_id: str) -> User:
    return user_service.get(user_id)

Vial supports some path parameter parsing as part of the invocation process. For example when using a UUID as a path parameter, Vial can convert it from a string to a UUID automatically:

from uuid import UUID

@app.get("/users/{user_id:uuid}")
def get_user(user_id: UUID) -> User:
    return user_service.get(user_id)

The following parsers are supported by default:

Parser	Type
str	str
bool	bool
int	int
float	float
decimal	decimal.Decimal
uuid	uuid.UUID

You can register your own parser like this:

@app.parser("list")
def list_parser(value: str) -> List[str]:
    return [value]


@app.get("/users/{user_id:list}")
def get_user(user_ids: List[str]) -> User:
    return user_service.get(user_id)

As parsers are bound directly to the registered route function, they have to be defined before the route function that uses one is registered.

Blueprints

As your application grows, you may want to split certain functionality amongst blueprints, similar to other popular frameworks like Flask.

You can define a blueprint like this:

# store.py
app = Blueprint()


@app.get("/stores/{store_id}")
def get_store(store_id: str) -> Store:
    return store_service.get(store_id)


# app.py
from stores import app as stores_app


app = Vial()

app.register_blueprint(stores_app)

Json Encoding

You can customize how Vial serializes / deserializes JSON objects by passing a custom encoder. The below example shows how to substitute the native JSON module with another library like simplejson:

import simplejson
from vial.app import Vial, Json


class SimpleJson(Json):
    @staticmethod
    def dumps(value: Any) -> str:
        return simplejson.dumps(value)

    @staticmethod
    def loads(value: str) -> Any:
        return simplejson.loads(value)

class JsonVial:
    json_class = SimpleJson


app = SimpleJsonVial()