res = requests.get(url=url,headers=headers, stream=True)
        total_size = int(res.headers['Content-Length'])
        size_mb = total_size/1048576
        print("文件大小为：",round(size_mb,2),"MB")
        with open(os.path.join(path,dirname,filename),'wb') as fw:
            for data in res.iter_content(chunk_size=1024*1024*10):
                size = size + 10
                if size >1024:
                    print("已经下载",size/1024,"GB，完成",round(100*size/size_mb,2),"%")
                else:
                    print("已经下载",size,"MB，完成",round(100*size/size_mb,2),"%")

                fw.write(data)
                fw.flush()
                os.fsync(fw.fileno())

下载一些文件，每次遇到大于600MB的就容易出现MemoryError错误，经过查询改进如上

可以强制每下载10MB就从内存保存到硬盘，彻底解决内存不足的问题，顺便显示下载进度

只加f.flush()，文件还是会一直在内存中，后面加os.fsync(f.fileno())，就会强制清除缓存至硬盘了。因为网络稳定，故无需加断点续传的功能了

参见：

https://stackoverflow.com/questions/16694907/download-large-file-in-python-with-requests

https://www.runoob.com/python/file-fileno.html

https://www.yiibai.com/python/os_fsync.html