import requests
import tqdm as tqdm
import os

url = 'http://mirrors.163.com/centos/8.3.2011/isos/x86_64/CentOS-8.3.2011-x86_64-boot.iso'
def download(url):
    filename = url.split('/')[-1]
    total_size = int(requests.head(url).headers['Content-Length'])
    if os.path.exists(filename):
        file_size = os.path.getsize(filename)
        if file_size < total_size:
            print('断点续传中。。。')
        elif file_size == total_size:
            print('文件已存在')
            exit(0)
    else:
        file_size = 0

    header = {'Range': 'bytes=%s-%s' % (file_size, total_size)}
    t = tqdm.tqdm(total=total_size, desc=filename, initial=file_size, unit='B', unit_scale=True)
    result = requests.get(url, headers=header, stream=True)

    with open(filename, 'ab') as f:
        for i in result.iter_content(chunk_size=1024):
            f.write(i)
            t.update(1024)
        t.close()

if __name__ == '__main__':
    url = 'http://mirrors.163.com/centos/8.3.2011/isos/x86_64/CentOS-8.3.2011-x86_64-boot.iso'
    download(url)