Retry Helper Module

smonad.retry - helpful utility and decorators for retrying operations.

class smonad.retry.NotReady(value)

Bases: smonad.types.ftry.Failure

Indicates target is not ready and retryable

class smonad.retry.StoppedClock

This class only exists to make it easier to test retries

set_times(times)

list of times for the self.time call to return the times can be a single value or be a value + side effect to trigger

example:

clock.set_times([100, 200, (300, lambda: Failure(“Uh oh!”), 400])

the 3rd invocation of clock.time() will return the Failure

example:

clock.set_times([100, 200, (300, function_with_side_effect), 400])

function_with_side_effect will be triggered the 3rd time clock.time() is invoked

sleep(seconds)

This sleep doesn’t actually sleep, so your tests run quickly!

class smonad.retry.SystemClock

This is just a wrapper around the built-in time.time that makes it much easier to test this module by mocking out time itself.

time()

Returns value of current UNIX epoch in seconds

smonad.retry.print_start_message(start_message, start_time)

Prints a start message and interpolates the start_time if the {start_time} placeholder is present in the message

example:

print_start_message(“Started operation at {start_time}”, start_time)

smonad.retry.retry(callable_object, timeout=600, delay=4, start_message=None, silent=False)

Retry calling the decorated function until it returns Success, Failure, or the retry count is exceeded Values of Success or Failure are returned immediately A NotReady means to retry the decorated function permitting that there are remaining retries loosely based on: http://www.saltycrane.com/blog/2009/11/trying-out-retry-decorator-python/ original from: http://wiki.python.org/moin/PythonDecoratorLibrary#Retry

This decorator expects the wrapped function to return any of three types Failure, NotReady, or Success Note that Failure and Success are imported from smonad.types.ftry and that NotReady is a subclass of Failure

Values of Success or Failure are returned immediately A NotReady means to retry the decorated function permitting that there are remaining retries

Parameters:

• callable_object (function) – object that can be called
• timeout (int) – maximum period, in seconds, to wait until an individual try succeeds
• delay (int) – initial delay between retries in seconds
• start_message (str) – message to print before executing first attempt, may contain placeholder {start_time} example start_message=”Started operation at {start_time}”
• silent (bool) – do not print start, end, or progress dots

smonad.retry.retry_decorator(timeout=600, delay=4, start_message=None, silent=False)

Decorator that wraps a callable with a retry loop. The callable should only return :class:Failure, :class:Success, or :class:NotReady

>>> deadline = time.time() + 300
>>> @retry_decorator()
... def wait_for_deadline():
...     now = time.time()
...     if now < deadline:
...         return NotReady("not ready yet")
...     else:
...         return Success("Ready!")
>>> wait_for_deadline()  
Success("Ready!")