Estou tentando baixar um arquivo do servidor FTP usando a biblioteca ftplib do Python 3.

Aqui está o código relevante

ftp = ftplib.FTP("ftp://library.daisy.org:21/User_****/Wise & Otherwise-22.zip") 
ftp.login("xxxxx", "xxxxxxx") 
ftp.cwd(path)
ftp.retrbinary("RETR " + filename, open(filename, 'wb').write)
ftp.quit()

Quando tento executar o script, o seguinte erro mostra

Traceback (most recent call last):
  File "reader.py", line 604, in <module>
    sp.process_user_choice()
  File "reader.py", line 72, in process_user_choice
    self.download_books()   File "reader.py", line 324, in download_books
    ftp = ftplib.FTP(all_urls[response]) 
  File "/usr/lib/python3.5/ftplib.py", line 118, in __init__
    self.connect(host)
  File "/usr/lib/python3.5/ftplib.py", line 153, in connect
    source_address=self.source_address)
  File "/usr/lib/python3.5/socket.py", line 694, in create_connection
    for res in getaddrinfo(host, port, 0, SOCK_STREAM):
  File "/usr/lib/python3.5/socket.py", line 733, in getaddrinfo
    for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno -2] Name or service not known

Algumas notas-

Eu tenho o URL e as credenciais corretasEstou atrás de um servidor proxy