A small scraper that uses ayncio to run lots of concurrent request on an API. However, it does use a sempaphore to limit the number of outgoing connection at one time.

async_multifetch.py

import asyncio
import json
from os import path

import aiohttp
import async_timeout

imdb_ids = ['0114319', '0112302', '0114576', '0113189', '0112346', '0112896', '0112453', 
            '0113987', '0112760', '0112641', '0114388', '0113101', '0112281', '0113845']
api_url = "http://www.omdbapi.com/?i=tt%s&plot=full&r=json"

all_plots = dict()

async def fetch(session, url):
    with async_timeout.timeout(10):
        async with session.get(url) as response:
            return await response.text()

async def retrieve_plot(imdb_id, count):
    # from what i've understood, every usage of this context adds one lock to the semaphore
    async with connection_limit: 
        async with aiohttp.ClientSession() as session: # async context for the client
            print("Fetching %i (%s)" % (count, imdb_id))
            response_text = await fetch(session, api_url % imdb_id)
            print("Got %i (%s)" % (count, imdb_id))
            try:
                plot = json.loads(response_text)["Plot"]
                all_plots[imdb_id] = plot
            except KeyError:
                pass

loop = asyncio.get_event_loop()
connection_limit = asyncio.Semaphore(10) # rate limit to 10 connections at a time
tasks = []
for i, imdb_id in enumerate(imdb_ids):
    task = asyncio.ensure_future(retrieve_plot(imdb_id, i))
    tasks.append(task)

loop.run_until_complete(asyncio.wait(tasks))

with open(path.join("plots.json", "wb") as jsonfile:
    json.dump(all_plots, jsonfile)