Python制作多线程下载器

在Python中制作多线程下载器通常会利用`threading`模块来实现并发下载，可以使用`requests`库来发送HTTP请求获取文件内容。下面是一个简单的例子，展示如何创建一个基本的多线程下载器：

import requests
import threading

class DownloaderThread(threading.Thread):
    def __init__(self, url, filename):
        threading.Thread.__init__(self)
        self.url = url
        self.filename = filename

    def run(self):
        response = requests.get(self.url, stream=True)
        with open(self.filename, 'wb') as file:
            for chunk in response.iter_content(chunk_size=8192):  
                if chunk:  # filter out keep-alive new chunks
                    file.write(chunk)

def download_parallel(urls, filenames, num_threads):
    threads = []
    for i in range(num_threads):
        thread_url = urls[i]
        thread_filename = filenames[i]
        thread = DownloaderThread(thread_url, thread_filename)
        threads.append(thread)
        thread.start()

    # 等待所有线程完成
    for thread in threads:
        thread.join()

# 使用示例
urls = ['http://example.com/file1', 'http://example.com/file2', 'http://example.com/file3']
filenames = ['file1.txt', 'file2.txt', 'file3.txt']
num_threads = min(len(urls), 5)  # 设置最大线程数不超过URL数量的一半
download_parallel(urls, filenames, num_threads)