问Concurrent.futures问题

EN

import requests, time
from concurrent.futures import ProcessPoolExecutor

sites = ["http://www.youtube.com"]

def get_one(site):
    resp = requests.get(site)
    size = len(resp.content)
    print(f"download {site} bytes from {site}")
    return size

def main():
    total_size = 0
    start = time.perf_counter()
    with ProcessPoolExecutor as exec:
        total_size = sum(exec.map(get_one, sites))
    end = time.perf_counter()
    for site in sites:
        
        total_size += size
        #print(f"downlded {size} bytes from {site}")
    #end = time.perf_counter()
    
    print(f"elapsed time: {end - start} seconds")
    print (f"downloaded a totla of {total_size} bytes")
    
    
if __name__== "__main__":
    main()