retry function/decorator

retry.py

import logging
import time
import traceback
from functools import wraps
from typing import Union, Type, Tuple, Optional, Callable, TypeVar

T = TypeVar("T")
logger = logging.getLogger(__name__)


def retry(
    exceptions: Union[Type[Exception], Tuple[Type[Exception], ...]],
    max_retries: int = 5,
    delay: int = 3,
    delay_multiplier: int = 2,
    exc_retry_condition: Optional[Callable[[Exception], bool]] = None,
    exc_retry_bypass_action_log: bool = True,
    exc_retry_bypass_action_raise: bool = True,
) -> Callable[[T], T]:
    """
    Retry calling the decorated function using an exponential backoff.

    Args:
        exceptions: A single or a tuple of Exceptions to trigger retry
        max_retries: Number of times to retry before failing.
        delay: Initial delay between retries in seconds.
        delay_multiplier: Delay multiplier (e.g. value of 2 will double the delay
            each retry).
        exc_retry_condition: A function where a raised exception will be passed
            as an argument. It checks if the retry mechanism should be bypassed
        exc_retry_bypass_action_log: when the exception retry condition is
            set but not satisfied, where a log message should be emitted
        exc_retry_bypass_action_raise: when the exception retry condition is
            set but not satisfied, where an exception should be emitted
    """

    def _retry_deco(f):
        @wraps(f)
        def f_retry(*args, **kwargs):
            attempt_num = 0
            mdelay = delay
            while attempt_num < max_retries:
                try:
                    return f(*args, **kwargs)
                except exceptions as e:
                    if exc_retry_condition is not None and not exc_retry_condition(e):
                        if exc_retry_bypass_action_log:
                            logger.error(
                                "Exception occurred for which retry is bypassed:",
                                exc_info=True,
                            )
                        if exc_retry_bypass_action_raise:
                            raise
                        else:
                            return
                    attempt_num += 1
                    logger.warning(
                        "Retry attempt #%d/%d in %d seconds ...\n%s",
                        attempt_num,
                        max_retries,
                        mdelay,
                        traceback.format_exc(limit=1),
                    )
                    time.sleep(mdelay)
                    mdelay *= delay_multiplier
            return f(*args, **kwargs)

        return f_retry

    return _retry_deco

Hi, something is wrong with the code, line 45:

(Pdb) pp exc_retry_condition(e)
*** TypeError: 'NoneType' object is not callable

How do you use it? I need to see the code to troubleshoot it.

I use it, as you describe it:

exceptions = (NetMikoTimeoutException, NetMikoAuthenticationException)
open_connection_retry = retry(exceptions_)(task.host.open_connection)
open_connection_retry("netmiko", configuration=task.nornir.config)_

I have commented problematic part of the code, but it looks there is another problem. After first exception (wrong password in inventory file)
NetMikoAuthenticationException, next log message is displayed:

Retry attempt #1/5 in 3 seconds ...

That is OK and during second retry next exception is trow:

nornir.core.exceptions.ConnectionAlreadyOpen: netmiko

It looks connection needs to be closed before nornir tries to opene it again.

BR Milan

Yeah, it is a known issue: nornir-automation/nornir#350
the fix for this didn't make it to the core yet.

is there a workaround?