Mount your HDFS with HDFS NFS Gateway and simply write with the normal write() method. Beware, that using this solution you won't be able to append!
Here's an implementation for you using urlopen and HdfsCli. To try it first install HdfsCli with pip install hdfs.
from urllib.request import urlopen
from hdfs import InsecureClient
# You can also use KerberosClient or custom client
namenode_address = 'your namenode address'
webhdfs_port = 'your webhdfs port' # default for Hadoop 2: 50070, Hadoop 3: 9870
user = 'your user name'
client = InsecureClient('http://' + namenode_address + ':' + webhdfs_port, user=user)
ftp_address = 'your ftp address'
hdfs_path = 'where you want to write'
with urlopen(ftp_address) as response:
content = response.read()
# You can also use append=True
# Further reference: https://hdfscli.readthedocs.io/en/latest/api.html#hdfs.client.Client.write
with client.write(hdfs_path) as writer: