urllib结合 concurrent.futures 多线程下载文件。

示例：

#!/usr/bin/env python3
# -*- coding:utf-8 -*-
#  @Time: 2020/12/16 10:42
#  @Author:zhangmingda
#  @File: urllib_multi_download.py
#  @Software: PyCharm
#  Description: 使用urllib 模块 实现多线程下载某个文件测试

from concurrent.futures import ThreadPoolExecutor, as_completed
from urllib.request import urlopen
from urllib.request import Request
from urllib.request import quote
import json
import math
import os

class DownLoader(object):
    def __init__(self):
        self.part_size = 1024 * 1024 * 10  # 分块下载大小
        self.part_thread_num = 10
        self.BUFFER_SIZE = 64 * 1024

    def download_part(self, encode_url, part_filename, offset, end_bytes):
        """
        :param encode_url:经过URL编码的网络地址 
        :param part_filename: 文件块儿名字
        :param offset: 下载字节起始点(包含)
        :param end_bytes: 下载字节结束点(包含)
        :return: (下载结果)
        """
        # 构造请求头
        range_header = {
            'Range': 'bytes=%s-%s' % (offset, end_bytes)
        }
        print(range_header)
        cur_task_ret = False
        expected_file_size = end_bytes - offset + 1
        part_req = Request(encode_url,headers=range_header)
        with open(part_filename, 'wb') as local_part_fd:
            with urlopen(part_req) as req_fd:
                while True:
                    # 一直从网络读数据
                    data = req_fd.read(self.BUFFER_SIZE)
                    if not data:
                        break
                    local_part_fd.write(data)
        if expected_file_size == os.stat(part_filename).st_size:
            print('%s 与预期块儿文件大小相符' % part_filename)
            cur_task_ret = True
            # break
        else:
            print('%s 与预期块儿文件大小 不符,预期%s字节,实际得到%s 字节' % (
            part_filename, expected_file_size, os.stat(part_filename).st_size))

        return {part_filename: cur_task_ret}

    def download(self, url):
        finally_filename = os.path.basename(url)
        # 将URL编码成%字符串格式
        encode_url = quote(url, safe=";/?:@&=+$,")
        print(encode_url)
        # 构造请求
        req = Request(encode_url)
        # 发起请求并且获取内容长度
        with urlopen(req) as fp:
            # print(json.dumps(dir(fp),indent=1))
            print(fp.getheaders())
            # length = fp.getheader('content-Range')
            length = fp.getheader('Content-Length')
            length = int(length)
            print(type(length))
            print('length:', length)
        
        # 分块任务列表
        thread_list = []
        # 每个块儿下载的结果
        multi_chunk_download_result = {}
        chunk_size = self.part_size
        # 计算需要下载的块儿个数
        chunk_count = int(math.ceil(length / float(chunk_size)))
        pool_args_list = []
        
        # 计算每个块儿请求的字节范围
        for i in range(chunk_count):
            offset = chunk_size * i
            end_bytes = min(chunk_size * (i + 1), length) - 1
            # 将一个文件划分的所有块儿任务，添加到任务列表
            part_num = i + 1
            part_filename = finally_filename + '.' + str(part_num)
            # 每个块儿请求的范围，块儿名字，加到线程参数列表
            pool_args_list.append((encode_url, part_filename, offset, end_bytes))
        
        # ********开始多线程下载数据，并获取下载结果**************
        # 构建线程池实例
        tp = ThreadPoolExecutor(max_workers=self.part_thread_num)
        # 全部添加到任务队列开始处理
        [thread_list.append(tp.submit(self.download_part, *args)) for args in pool_args_list]
        # 等待所有线程结束，获取全部线程的执行结果
        [multi_chunk_download_result.update(part_thread.result()) for part_thread in as_completed(thread_list)]

        # 下载总结
        print('下载总结')
        # 如果任务数和块儿数对不上，报一下出入
        if len(multi_chunk_download_result) != chunk_count:
            raise RuntimeError(
                "%s part miss,expect=%d,actual=%d" % (finally_filename, chunk_count, len(multi_chunk_download_result)))
        # 如果任务都完毕，检查是否有失败的块儿
        for item in multi_chunk_download_result.keys():
            if not multi_chunk_download_result[item]:
                raise RuntimeError("%s part upload has fail" % item)
        # 都OK 整合文件
        with open(finally_filename, 'wb') as local_fd:
            for i in range(chunk_count):
                part_filename = finally_filename + '.' + str(i + 1)
                with open(part_filename, 'rb') as part_fd:
                    while True:
                        bytes_data = part_fd.read(self.BUFFER_SIZE)
                        if not bytes_data:
                            break
                        local_fd.write(bytes_data)
        
        if length == os.stat(finally_filename).st_size:
            print('%s  下载完成，文件大小相符' % finally_filename)
            for part_filename in multi_chunk_download_result.keys():
                os.remove(part_filename)
        else:
            print('%s  下载完成，但大小不符,content_length:%s  下载后大小 %s' % (finally_filename, length,os.stat(finally_filename).st_size ))


if __name__ == '__main__':
    downloader = DownLoader()
    url = 'https://ks3-cn-beijing.ksyun.com/zhangmingda/111-3333333.Python安装与命令行操作.mp4'
    print(url)
    downloader.download(url)