Call a function which returns True/False to indicate success or failure. On failure, wait, and try the function again. On repeated failures, wait longer between each successive attempt. If the decorator runs out of attempts, then it gives up and returns False, but you could just as easily raise some exception.
import time
import math
#
# Retry decorator with exponential backoff
#
# Call a function which returns True/False to indicate success or failure. On
# failure, wait, and try the function again. On repeated failures, wait longer
# between each successive attempt. If the decorator runs out of attempts, then
# it gives up and returns False, but you could just as easily raise some
# exception.
#
# Source: https://wiki.python.org/moin/PythonDecoratorLibrary#Retry
#
def retry(tries, delay=3, backoff=2):
"""Retries a function or method until it returns True.
delay sets the initial delay in seconds, and backoff sets the factor by which
the delay should lengthen after each failure. backoff must be greater than 1,
or else it isn't really a backoff. tries must be at least 0, and delay
greater than 0."""
if backoff <= 1:
raise ValueError("backoff must be greater than 1")
tries = math.floor(tries)
if tries < 0:
raise ValueError("tries must be 0 or greater")
if delay <= 0:
raise ValueError("delay must be greater than 0")
def deco_retry(f):
def f_retry(*args, **kwargs):
mtries, mdelay = tries, delay # make mutable
rv = f(*args, **kwargs) # first attempt
while mtries > 0:
if rv is True: # Done on success
return True
mtries -= 1 # consume an attempt
time.sleep(mdelay) # wait...
mdelay *= backoff # make future wait longer
rv = f(*args, **kwargs) # Try again
return False # Ran out of tries :-(
return f_retry # true decorator -> decorated function
return deco_retry # @retry(arg[, ...]) -> true decorator