retry.py

# http://wiki.python.org/moin/PythonDecoratorLibrary#Retry

import math
import time

# Retry decorator with exponential backoff
def retry(tries, delay=1, backoff=2):
  """Retries a function or method until it returns True.
 
  delay sets the initial delay, and backoff sets how much 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 == True or type(rv) == str: # Done on success ..
          return rv

        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

@retry(2)
def f(x):
    if x > 0:
        print "False"
        return False
    return True

if __name__ == '__main__':
    f(3)