transfer.py 文件源码

def start(self):
        assert not self.started, "File download has already been started, and cannot be started again"

        # initialize the requests session, with backoff-retries enabled
        self.session = requests.Session()
        self.session.mount('http://', HTTPAdapter(max_retries=retries))
        self.session.mount('https://', HTTPAdapter(max_retries=retries))

        # initiate the download, check for status errors, and calculate download size
        self.response = self.session.get(
            self.source, stream=True, timeout=self.timeout)
        self.response.raise_for_status()
        self.total_size = int(self.response.headers['content-length'])

        self.started = True