pysftp gives pysftp.exceptions.ConnectionException: (host, port) with no details on it - python-2.7

Question

I'm trying to connect to sftp server with pysftp library. Here is my code:
import pysftp
cnopts = pysftp.CnOpts()
cnopts.hostkeys = None
with pysftp.Connection("sftp://host", "login", "password", cnopts=cnopts) as sftp:
sftp.listdir()
It gives me exception:
pysftp.exceptions.ConnectionException: ('host', port)
But I have no clue what this exception means and what the problem is.

Answer 1

You don't have much explanation because this library has bugs. See the source code on BitBucket.
The ConnectionException class is not well implemented:
class ConnectionException(Exception):
"""Exception raised for connection problems
Attributes:
message -- explanation of the error
"""
def __init__(self, host, port):
# Call the base class constructor with the parameters it needs
Exception.__init__(self, host, port)
self.message = 'Could not connect to host:port. %s:%s'
As you can see, the format 'Could not connect to host:port. %s:%s' is not filled with the host and port values.
However, the name of the exception is clear: you have a connection error.
The details of the error are, unfortunately, lost:
def _start_transport(self, host, port):
'''start the transport and set the ciphers if specified.'''
try:
self._transport = paramiko.Transport((host, port))
# Set security ciphers if set
if self._cnopts.ciphers is not None:
ciphers = self._cnopts.ciphers
self._transport.get_security_options().ciphers = ciphers
except (AttributeError, socket.gaierror):
# couldn't connect
raise ConnectionException(host, port)
You can try to get the last error (not sure):
import sys
sys.exc_info()
note: I suggest you to use another library (for instance Paramiko).