Pass Flask route parameters into a decorator

Question

I have written a decorator that attempts to check we have post data for a Flask POST route:

Here's my decorator:

def require_post_data(required_fields=None):
    def decorator(f):
        @wraps(f)
        def decorated_function(*args, **kwargs):
            for required_field in required_fields:
                if not request.form.get(required_field, None):
                    return jsonify({"error": "Missing %s from post data." %
                                    required_field}), 400
            else:
                if not request.form:
                    return jsonify({"error": "No post data, aborting."}), 400
            return f(*args, **kwargs)
        return decorated_function
    return decorator

And I have two routes, with with a URL param and the other without:

from flask import Blueprint, jsonify, request

mod = Blueprint('contacts', __name__, url_prefix='/contacts')


@mod.route('/', methods=['POST'])
@require_post_data(['customer_id', 'some_other_required_field'])
def create_contact():
    # Do some business


@mod.route('/<int:contact_id>', methods=['POST'])
@require_post_data
def update_contact(contact_id):
    # Do some business

When I run a test that hits update_contact, I'm getting the following exception:

TypeError: decorator() got an unexpected keyword argument 'contact_id'

But it looks like create_contact is working as expected.

Why is contact_id being passed into decorator()?

Answer 1

I believe you're just missing one thing, which is to actually call require_post_data to produce a decorator function in the update_contact route. This should fix it:

@mod.route('/<int:contact_id>', methods=['POST'])
@require_post_data() # <- note the parens
def update_contact(contact_id):
    # Do some business

The detailed explanation is that what you expected to happen (and what is happening in create contact) is that the the view function is being modified by the decorator produced by require_post_data. In your update_contact above, what is actually happening is that the view function is being passed to require_post_data itself and simply used as the value of the required_fields parameter. This doesn't cause an error so require_post_data happily returns decorator which is then routed to when you hit /<int>, causing it to be passed contact_id as a keyword argument, resulting in the error you saw.