How to Speed Up Downloads with ThreadPoolExecutor in Python

import time
import threading
from concurrent.futures import ThreadPoolExecutor

def download_file(file_id):
    """Simulate fetching a file by sleeping briefly."""
    time.sleep(0.2)  # pretend network latency
    return f"file_{file_id}"

def sequential_downloads(num_files):
    """Process files one at a time."""
    start = time.perf_counter()
    results = [download_file(i) for i in range(num_files)]
    elapsed = time.perf_counter() - start
    return results, elapsed

def concurrent_downloads(num_files):
    """Process files in parallel using a thread pool."""
    start = time.perf_counter()
    with ThreadPoolExecutor(max_workers=min(num_files, 4)) as executor:
        results = list(executor.map(download_file, range(num_files)))
    elapsed = time.perf_counter() - start
    return results, elapsed

if __name__ == "__main__":
    file_count = 8

    seq_results, seq_time = sequential_downloads(file_count)
    print(f"Sequential: {seq_time:.3f}s — files: {seq_results}")

    con_results, con_time = concurrent_downloads(file_count)
    print(f"Concurrent: {con_time:.3f}s — files: {con_results}")

    speedup = seq_time / con_time if con_time > 0 else float("inf")
    print(f"Speedup factor: {speedup:.2f}x")