qval 0.1.6

This module provides convenient API for verifying query parameters.

Qval | Query param validation library

Installation

$ pip install qval

Basic usage

You can use Qval as both a function and a decorator. Function validate() accepts 3 positional arguments and 1 named:

# qval.py
def validate(
    # Request instance. Must be a dictionary or support request interface.
    request: Union[Request, Dict[str, str]],
    # Dictionary of (param_name -> `Validator()` object).
    validators: Dict[str, Validator] = None,
    # Provide true if you want to access all parameters from the request through the context object.
    box_all: bool = True,
    # Factories that will be used to convert parameters to python objects (callable[str, any] -> object).
    **factories,
) -> QueryParamValidator: 

Imagine you have a RESTful calculator with an endpoint called /api/divide. You can use validate() to automatically convert parameters to python objects and then validate them:

from qval import validate
...

def division_view(request):
    """
    GET /api/divide?
    param a     : int
    param b     : int, nonzero
    param token : string, length = 12
       
    Example: GET /api/divide?a=10&b=2&token=abcdefghijkl -> 200, {"answer": 5}
    """
    # Parameter validation occurs in the context manager.
    # If validation fails or user code throws an error, context manager
    # will raise InvalidQueryParamException or APIException respectively.
    # In Django Rest Framework, these exceptions will be processed and result 
    # in error codes (400 and 500) on the client side.
    params = (
        # `a` and `b` must be integers
        # Note: in order to get a nice error message on the client side,
        # you factory should raise either ValueError or TypeError
        validate(request, a=int, b=int)
        # `b` must be anything but zero
        .nonzero("b")
        # The `transform` callable will be applied to parameter before the check.
        # In this case we'll get `token`'s length and check if it is equal to 12.
        .eq("token", 12, transform=len)
    )
    with params as p:
        return Response({"answer": p.a // p.b})

// GET /api/divide?a=10&b=2&token=abcdefghijkl
// Browser:
{
  "answer": 5
}

Sending b = 0 to this endpoint will result in the following message on the client side:

// GET /api/divide?a=10&b=0&token=abcdefghijkl
{
  "error": "Invalid `b` value: 0."
}

If you have many parameters and custom validators, it's better to use the @qval() decorator:

# validators.py
from decimal import Decimal
from qval import Validator
...

purchase_factories = {"price": Decimal, "item_id": int, "token": None}
purchase_validators = {
    "price": Validator(lambda x: x > 0),
    "token": Validator(lambda x: len(x) == 12),
    "item_id": Validator(lambda x: x >= 0),
}

# views.py
from qval import qval
from validators import *
...

# Any function or method wrapped with `qval()` must accept request as 
# either first or second argument, and parameters as last.
@qval(purchase_factories, purchase_validators)
def purchase_view(request, params):
    """
    GET /api/purchase?
    param item_id : int, positive
    param price   : float, greater than zero
    param token   : string, len == 12

    Example: GET /api/purchase?item_id=1&price=5.8&token=abcdefghijkl
    """
    print(f"{params.item_id} costs {params.price}$.")
    ...

Framework-specific instructions:

1. Django Rest Framework works straight out of the box. Simply add @qval() to your views or use validate() inside.

2. For Django without DRF you may need to add exception handler to settings.MIDDLEWARE. Qval attempts to do it automatically if DJANO_SETTINGS_MODULE is set. Otherwise you'll see the following message:

   WARNING:root:Unable to add APIException middleware to the MIDDLEWARE list. Django does not 
   support APIException handling without DRF integration. Define DJANGO_SETTINGS_MODULE or 
   add 'qval.framework_integration.HandleAPIExceptionDjango' to the MIDDLEWARE list.
   

   Take a look at plain Django example here.

3. If you are using Flask, you will need to setup exception handlers:

   from flask import Flask
   from qval.framework_integration import setup_flask_error_handlers
   ...
   app = Flask(__name__)
   setup_flask_error_handlers(app)
   

   Since request in Flask is a global object, you may want to curry @qval() before usage:

   from flask import request
   from qval import qval_curry
   
   # Firstly, curry `qval()`
   qval = qval_curry(request)
   ...
   
   # Then use it as decorator.
   # Note: you view now must accept request as first argument
   @qval(...)
   def view(request, params): 
   ...
   

   Check out the full Flask example in examples/flask-example.py.
   

   You can run the example using the command below:

   $ PYTHONPATH=. FLASK_APP=examples/flask-example.py flask run
   

4. Similarly to Flask, with Falcon you will need to setup error handlers:

   import falcon
   from qval.framework_integration import setup_falcon_error_handlers
   ...
   app = falcon.API()
   setup_falcon_error_handlers(app)
   

   Full Falcon example can be found here: examples/falcon-example.py.
   

   Use the following command to run the app:

   $ PYTHONPATH=. python examples/falcon-example.py
   

TODO:

1. Write docs
2. Add better error messages