"""Decorators module."""
import logging
import time
from datetime import timedelta
from functools import wraps
from spicerack.exceptions import SpicerackError
logger = logging.getLogger(__name__) # pylint: disable=invalid-name
[docs]def ensure_wrap(func):
"""Decorator to wrap other decorators to allow to call them both with and without arguments.
Arguments:
func: the decorated function, it must be a decorator. A decorator that accepts only one positional argument
that is also a callable is not supported.
"""
@wraps(func)
def wrapper(*args, **kwargs):
"""Decorator wrapper."""
if len(args) == 1 and not kwargs and callable(args[0]): # Called without arguments
return func(args[0])
return lambda real_func: func(real_func, *args, **kwargs) # Called with arguments
return wrapper
# TODO: 'func=None' is a workaround for https://github.com/PyCQA/pylint/issues/259, restore it to 'func, *' once fixed.
[docs]@ensure_wrap
def retry(func=None, tries=3, delay=timedelta(seconds=3), backoff_mode='exponential', exceptions=(SpicerackError,)):
"""Decorator to retry a function or method if it raises certain exceptions with customizable backoff.
Note:
The decorated function or method must be idempotent to avoid unwanted side effects.
It can be called with or without arguments, in the latter case all the default values will be used.
Arguments:
func (function, method): the decorated function.
tries (int, optional): the number of times to try calling the decorated function or method before giving up.
Must be a positive integer.
delay (datetime.timedelta, optional): the initial delay for the first retry, used also as the base for the
backoff algorithm.
backoff_mode (str, optional): the backoff mode to use for the delay, available values are:
constant: delay => 3, 3, 3, 3, 3, ...;
linear: delay * N => 3, 6, 9, 12, 15, ...; N in [1, tries]
power: delay * 2^N => 3, 6, 12, 24, 48, ...; N in [0, tries - 1]
exponential: delay^N => 3, 9, 27, 81, 243, ...; N in [1, tries], delay must be > 1.
exceptions (type, tuple, optional): the decorated function call will be retried if it fails until it succeeds
or `tries` attempts are reached. A retryable failure is defined as raising any of the exceptions listed.
Returns:
function: the decorated function.
"""
@wraps(func)
def wrapper(*args, **kwargs):
"""Decorator."""
if backoff_mode not in ('constant', 'linear', 'power', 'exponential'):
raise ValueError('Invalid backoff_mode: {mode}'.format(mode=backoff_mode))
if backoff_mode == 'exponential' and delay.total_seconds() < 1:
raise ValueError(
'Delay must be greater than 1 if backoff_mode is exponential, got {delay}'.format(delay=delay))
if tries < 1:
raise ValueError('Tries must be a positive integer, got {tries}'.format(tries=tries))
attempt = 0
while attempt < tries - 1:
attempt += 1
try:
return func(*args, **kwargs) # Call the decorated function or method
except exceptions as e:
sleep = get_backoff_sleep(backoff_mode, delay.total_seconds(), attempt)
logger.warning("Failed to call '%s.%s' [%d/%d, retrying in %.2fs]: %s",
func.__module__, func.__name__, attempt, tries, sleep, e)
time.sleep(sleep)
return func(*args, **kwargs)
return wrapper
[docs]def get_backoff_sleep(backoff_mode, base, index):
"""Calculate the amount of sleep for this attempt.
Arguments:
backoff_mode (str): the backoff mode to use for the delay, see the documentation for retry().
base (int, float): the base for the backoff algorithm.
index (int): the index to calculate the Nth sleep time for the backoff.
Return:
int, float: the amount of sleep to perform for the backoff.
"""
if backoff_mode == 'constant':
sleep = base
elif backoff_mode == 'linear':
sleep = base * index
elif backoff_mode == 'power':
sleep = base * 2 ** (index - 1)
elif backoff_mode == 'exponential':
sleep = base ** index
else:
raise ValueError('Invalid backoff_mode: {mode}'.format(mode=backoff_mode))
return sleep