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Flask-Pydantic

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Flask extension for integration of the awesome pydantic package with Flask.

Installation

python3 -m pip install Flask-Pydantic

Basics

URL query and body parameters

validate decorator validates query, body and form-data request parameters and makes them accessible two ways:

  1. Using validate arguments, via flask's request variable
parameter typerequest attribute name
queryquery_params
bodybody_params
formform_params
  1. Using the decorated function argument parameters type hints

URL path parameter

If you use annotated path URL path parameters as follows


@app.route("/users/<user_id>", methods=["GET"])
@validate()
def get_user(user_id: str):
    pass

flask_pydantic will parse and validate user_id variable in the same manner as for body and query parameters.

Additional validate arguments

For more details see in-code docstring or example app.

Usage

Example 1: Query parameters only

Simply use validate decorator on route function.

:exclamation: Be aware that @app.route decorator must precede @validate (i. e. @validate must be closer to the function declaration).

from typing import Optional
from flask import Flask, request
from pydantic import BaseModel

from flask_pydantic import validate

app = Flask("flask_pydantic_app")

class QueryModel(BaseModel):
  age: int

class ResponseModel(BaseModel):
  id: int
  age: int
  name: str
  nickname: Optional[str] = None

# Example 1: query parameters only
@app.route("/", methods=["GET"])
@validate()
def get(query: QueryModel):
  age = query.age
  return ResponseModel(
    age=age,
    id=0, name="abc", nickname="123"
    )
<a href="example_app/example.py"> See the full example app here </a>

-> {"id": 0, "age": 20, "name": "abc", "nickname": "123"}

Example 2: URL path parameter

@app.route("/character/<character_id>/", methods=["GET"])
@validate()
def get_character(character_id: int):
    characters = [
        ResponseModel(id=1, age=95, name="Geralt", nickname="White Wolf"),
        ResponseModel(id=2, age=45, name="Triss Merigold", nickname="sorceress"),
        ResponseModel(id=3, age=42, name="Julian Alfred Pankratz", nickname="Jaskier"),
        ResponseModel(id=4, age=101, name="Yennefer", nickname="Yenn"),
    ]
    try:
        return characters[character_id]
    except IndexError:
        return {"error": "Not found"}, 400

Example 3: Request body only

class RequestBodyModel(BaseModel):
  name: str
  nickname: Optional[str] = None

# Example2: request body only
@app.route("/", methods=["POST"])
@validate()
def post(body: RequestBodyModel):
  name = body.name
  nickname = body.nickname
  return ResponseModel(
    name=name, nickname=nickname,id=0, age=1000
    )
<a href="example_app/example.py"> See the full example app here </a>

Example 4: BOTH query paramaters and request body

# Example 3: both query paramters and request body
@app.route("/both", methods=["POST"])
@validate()
def get_and_post(body: RequestBodyModel,query: QueryModel):
  name = body.name # From request body
  nickname = body.nickname # From request body
  age = query.age # from query parameters
  return ResponseModel(
    age=age, name=name, nickname=nickname,
    id=0
  )
<a href="example_app/example.py"> See the full example app here </a>

Example 5: Request form-data only

class RequestFormDataModel(BaseModel):
  name: str
  nickname: Optional[str] = None

# Example2: request body only
@app.route("/", methods=["POST"])
@validate()
def post(form: RequestFormDataModel):
  name = form.name
  nickname = form.nickname
  return ResponseModel(
    name=name, nickname=nickname,id=0, age=1000
    )
<a href="example_app/example.py"> See the full example app here </a>

Modify response status code

The default success status code is 200. It can be modified in two ways

# necessary imports, app and models definition
...

@app.route("/", methods=["POST"])
@validate(body=BodyModel, query=QueryModel)
def post():
    return ResponseModel(
            id=id_,
            age=request.query_params.age,
            name=request.body_params.name,
            nickname=request.body_params.nickname,
        ), 201

@app.route("/", methods=["POST"])
@validate(body=BodyModel, query=QueryModel, on_success_status=201)
def post():
    ...

Status code in case of validation error can be modified using FLASK_PYDANTIC_VALIDATION_ERROR_STATUS_CODE flask configuration variable.

Using the decorated function kwargs

Instead of passing body and query to validate, it is possible to directly defined them by using type hinting in the decorated function.

# necessary imports, app and models definition
...

@app.route("/", methods=["POST"])
@validate()
def post(body: BodyModel, query: QueryModel):
    return ResponseModel(
            id=id_,
            age=query.age,
            name=body.name,
            nickname=body.nickname,
        )

This way, the parsed data will be directly available in body and query. Furthermore, your IDE will be able to correctly type them.

Model aliases

Pydantic's alias feature is natively supported for query and body models. To use aliases in response modify response model

def modify_key(text: str) -> str:
    # do whatever you want with model keys
    return text


class MyModel(BaseModel):
    ...
    model_config = ConfigDict(
        alias_generator=modify_key,
        populate_by_name=True
    )

and set response_by_alias=True in validate decorator

@app.route(...)
@validate(response_by_alias=True)
def my_route():
    ...
    return MyModel(...)

Example app

For more complete examples see example application.

Configuration

The behaviour can be configured using flask's application config FLASK_PYDANTIC_VALIDATION_ERROR_STATUS_CODE - response status code after validation error (defaults to 400)

Additionally, you can set FLASK_PYDANTIC_VALIDATION_ERROR_RAISE to True to cause flask_pydantic.ValidationError to be raised with either body_params, form_params, path_params, or query_params set as a list of error dictionaries. You can use flask.Flask.register_error_handler to catch that exception and fully customize the output response for a validation error.

Contributing

Feature requests and pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

TODOs: