Parellizing API calls with python asyncio

Some thoughts on asyncio and a code example where I refactored the code to use it.

• Asyncio is one of the three ways to parallelize API calls with python.  Asyncio was available starting in python 3.4.
• https://stackoverflow.com/questions/49663091/how-to-parallelize-python-api-calls
• Why are all the examples online having to do with asyncio and aiohttp?  You can use regular python 'requests' library with asyncio.
• I hadn't explicitly used the unpack * operator to unpack a list into separate expressions in python yet:
• https://realpython.com/async-io-python/#the-asyncawait-syntax-and-native-coroutines
• https://stackoverflow.com/questions/71235585/passing-in-a-list-of-functions-to-asyncio-gather
• THIS article used the explicit word unpack and not just use the * and not explain what it was - https://superfastpython.com/asyncio-gather/
• No event loop in current thread, create if doesn't exist:
• https://stackoverflow.com/questions/46727787/runtimeerror-there-is-no-current-event-loop-in-thread-in-async-apscheduler

The code example refactors the get_results function to use asyncio.  It uses both _get_info_lookup and _retrieve_aggregation_results functions; their implementation details are not shown.  _retrieve_aggregation_results ultimately makes the HTTP API call to get data from an external source.

Old Code Snippet:

def get_results(metadata, granularity):
    [some code]
    combined_result = {}
    info_lookup_list = _get_info_lookup(granularity)
    for retrieval_info in info_lookup_list:
        result_info = _retrieve_aggregation_results(retrieval_info, metadata)
        combined_result[retrieval_info['result_key']] = result_info['result']
    [some code]

Refactored Code Snippet:

async def _retrieve_aggregation_results_async_coroutine(retrieval_info, metadata):
    """
    Native coroutine, modern syntax. Retrieve aggregation results.
    Return a tuple=(
        <retrieval_info['result_key']>, (String) e.g. daily, hourly
        <dictionary of lists> (Dictionary) e.g. { result_list_1, result_list_2, result_list_3 }
    )
    """
    result_info = _retrieve_aggregation_results(retrieval_info, metadata)
    return (retrieval_info['result_key'], result_info)

async def _create_aggregation_results_async_scheduler(info_lookup_list, metadata):
    """
    Create an async scheduler for retrieving aggregation results.
    Return a list of tuples for each task created:
    tuple=(
        <retrieval_info['result_key']>, (String) e.g. daily, hourly
        <dictionary of lists> (Dictionary) e.g. { result_list_1, result_list_2, result_list_3 }
    )
    """
    request_list = []

    for retrieval_info in info_lookup_list:
        # in Python 3.6 or lower, use asyncio.ensure_future() instead of create_task
        task = asyncio.ensure_future(_retrieve_aggregation_results_async_coroutine(retrieval_info, metadata))
        request_list.append(task)

    # gather all results by unpacking the request_list and passing them each as a parameter to asyncio.gather()
    result_list = await asyncio.gather(*request_list)
    return result_list

def get_results(metadata, granularity):
    [some code]
    
    info_lookup_list = _get_info_lookup(granularity)
    
    # in Python 3.6 or lower, use ayncio.get_event_loop and run_until_complete instead of asyncio.run
    try:
        event_loop = asyncio.get_event_loop()
    except RuntimeError as e:
        if str(e).startswith('There is no current event loop in thread'):
            event_loop = asyncio.new_event_loop()
            asyncio.set_event_loop(event_loop)

    result_list = event_loop.run_until_complete(_create_aggregation_results_async_scheduler(info_lookup_list, metadata))

    for tuple_result in result_list:
        # tuple_result[0] is a String that holds the result_key (e.g. daily, hourly)
        # tuple_result[1] is a Dictionary of lists (e.g. { result_list_1, result_list_2, result_list_3 })
        result_key = tuple_result[0]
        performance_result = tuple_result[1]

        combined_result[result_key] = performance_result
        
    [some code]