SSHException handled but traceback is still displayed in stderr

I am trying to handle the SSHException using the try/except block. It’s handled but the traceback is still printed out! Even if I try Exception or BaseException instead of SSHException, it’s handled but I still get the traceback displayed in the stderr.

I also tried removing Paramiko’s exception and to use the one in Netmiko (I know it’s the same as the one in paramiko)

import sys

from netmiko import ConnectHandler
from netmiko.ssh_exception import (
    NetmikoAuthenticationException,
    NetmikoTimeoutException,
    # SSHException
)
from paramiko.ssh_exception import SSHException

device = {
    "device_type": "cisco_ios",
    "ip": "192.168.1.1",
    "username": "cisco",
    "password": "cisco",
    "secret": "",
    "fast_cli": False,
}

try:
    print(f"Connecting to {device['ip']}...")
    with ConnectHandler(**device) as conn:
        print(f"Connected to {conn.host}:{conn.port}")
        facts = conn.send_command(command_string="show version", use_textfsm=True)
except (
    SSHException,
    NetmikoAuthenticationException,
    NetmikoTimeoutException,
    ConnectionResetError,
    TimeoutError,
) as e:
    print(f"Connection to {device['ip']} failed: {e}", file=sys.stderr)
else:
    print(facts)

Exception: Error reading SSH protocol banner
Traceback (most recent call last):
  File "C:\Users\username\AppData\Roaming\Python\Python39\site-packages\paramiko\transport.py", line 2211, in _check_banner
    buf = self.packetizer.readline(timeout)
  File "C:\Users\username\AppData\Roaming\Python\Python39\site-packages\paramiko\packet.py", line 380, in readline
    buf += self._read_timeout(timeout)
  File "C:\Users\username\AppData\Roaming\Python\Python39\site-packages\paramiko\packet.py", line 622, in _read_timeout
    raise socket.timeout()
socket.timeout

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\username\AppData\Roaming\Python\Python39\site-packages\paramiko\transport.py", line 2039, in run
    self._check_banner()
  File "C:\Users\username\AppData\Roaming\Python\Python39\site-packages\paramiko\transport.py", line 2215, in _check_banner
    raise SSHException(
paramiko.ssh_exception.SSHException: Error reading SSH protocol banner

I want to prevent the traceback being printed out to the stderr.

Thank you!

[Tes3awy]

@Tes3awy Let me know if the logging fix works or not.

I am pretty confident about the underlying cause of the issue being Paramiko using threading in a certain context (as I have seen this issue before).

Yes, using logging does fix the issue. What I actually did is that I added the following lines to my script

import logging

logging.basicConfig(filename="netmiko.log", level=logging.WARNING)
logger = logging.getLogger("netmiko")

However, if you don’t need a log file to be created in the cwd

import logging

logger = logging.getLogger("paramiko")  # paramiko not netmiko
logger.addHandler(logging.NullHandler())

You can also refer to this official Python documentation link for the second method.

Thanks a lot @ktbyers. Have a great day ahead!

[ktbyers]

@Tes3awy Let me know if the logging fix works or not.

I am pretty confident about the underlying cause of the issue being Paramiko using threading in a certain context (as I have seen this issue before).