MVE for performance bug in `flask_restful.fields.Url`

mve.py

#!/usr/bin/env python3
from flask import Flask
from flask_restful import fields, reqparse, Api, Resource, marshal
import time

app = Flask(__name__)
api = Api(app)

items_fields = {
    'info': fields.String,
    'large_info_url': fields.Url('large_info'),
}

items_fields_without_url = {
    'info': fields.String,
}

# Large object, created outside the code whose performance is measured
LARGE_INFO = [ 'lots_of_information_goes_here' for _ in range(0, 100000) ]

# Constant list of items to return
items = [ {
    'id': 0,
    'info': 'hello',
    'large_info': LARGE_INFO,
} ]

parser = reqparse.RequestParser()
parser.add_argument('omit_url', type=bool, help='Do not serialize URLs',
    default=False)

class Items(Resource):
    def get(self):
        args = parser.parse_args()
        if args['omit_url']:
            return marshal(items, items_fields_without_url)
        else:
            return marshal(items, items_fields)

class LargeInfo(Resource):
    def get(self, id):
        pass

api.add_resource(Items,
    '/items/',
    endpoint='items')
api.add_resource(LargeInfo,
    '/items/<id>/large_info',
    endpoint='large_info')

if __name__=='__main__':
    app = app.test_client()
    started_at = time.time()
    app.get('/items/')
    ended_at = time.time()
    print('GET w/  URL took: {0}s'.format(ended_at - started_at))

    started_at = time.time()
    app.get('/items/', data = { 'omit_url': True })
    ended_at = time.time()
    print('GET w/o URL took: {0}s'.format(ended_at - started_at))

output

GET w/  URL took: 1.2314190864562988s
GET w/o URL took: 0.0008442401885986328s