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riprova (meaning retry in Italian) is a small, general-purpose and versatile Python_ library that provides retry mechanisms with multiple backoff strategies for any sort of failed operations.

It's domain agnostic, highly customizable, extensible and provides a minimal API that's easy to instrument in any code base via decorators, context managers or raw API consumption.

For a brief introduction about backoff mechanisms for potential failed operations, read this article_.

Features

  • Retry decorator for simple and idiomatic consumption.
  • Simple Pythonic programmatic interface.
  • Maximum retry timeout support.
  • Supports error whitelisting_ and blacklisting_.
  • Supports custom error evaluation_ retry logic (useful to retry only in specific cases).
  • Automatically retry operations on raised exceptions.
  • Supports asynchronous coroutines_ with both async/await and yield from syntax.
  • Configurable maximum number of retry attempts.
  • Highly configurable supporting max retries, timeouts or retry notifier callback.
  • Built-in backoff strategies: constant, fibonacci_ and exponential_ backoffs.
  • Supports sync/async context managers.
  • Pluggable custom backoff strategies.
  • Lightweight library with almost zero embedding cost.
  • Works with Python +2.6, 3.0+ and PyPy.

Backoff strategies

List of built-in backoff strategies.

  • Constant backoff_
  • Fibonacci backoff_
  • Exponential backoff_

You can also implement your own one easily. See ConstantBackoff_ for an implementation reference.

Installation

Using pip package manager (requires pip 1.9+. Upgrade it running: pip install -U pip):

.. code-block:: bash

pip install -U riprova

Or install the latest sources from Github:

.. code-block:: bash

pip install -e git+git://github.com/h2non/riprova.git#egg=riprova

API

  • riprova.retry_
  • riprova.Retrier_
  • riprova.AsyncRetrier_
  • riprova.Backoff_
  • riprova.ConstantBackoff_
  • riprova.FibonacciBackoff_
  • riprova.ExponentialBackoff_
  • riprova.ErrorWhitelist_
  • riprova.ErrorBlacklist_
  • riprova.add_whitelist_error_
  • riprova.RetryError_
  • riprova.RetryTimeoutError_
  • riprova.MaxRetriesExceeded_
  • riprova.NotRetriableError_

.. _riprova.retry: http://riprova.readthedocs.io/en/latest/api.html#riprova.retry .. _riprova.Retrier: http://riprova.readthedocs.io/en/latest/api.html#riprova.Retrier .. _riprova.AsyncRetrier: http://riprova.readthedocs.io/en/latest/api.html#riprova.AsyncRetrier .. _riprova.Backoff: http://riprova.readthedocs.io/en/latest/api.html#riprova.Backoff .. _riprova.ConstantBackoff: http://riprova.readthedocs.io/en/latest/api.html#riprova.ConstantBackoff .. _riprova.FibonacciBackoff: http://riprova.readthedocs.io/en/latest/api.html#riprova.FibonacciBackoff .. _riprova.ExponentialBackoff: http://riprova.readthedocs.io/en/latest/api.html#riprova.ExponentialBackoff .. _riprova.ErrorWhitelist: http://riprova.readthedocs.io/en/latest/api.html#riprova.ErrorWhitelist .. _riprova.ErrorBlacklist: http://riprova.readthedocs.io/en/latest/api.html#riprova.ErrorBlacklist .. _riprova.add_whitelist_error: http://riprova.readthedocs.io/en/latest/api.html#riprova.add_whitelist_error .. _riprova.RetryError: http://riprova.readthedocs.io/en/latest/api.html#riprova.RetryError .. _riprova.RetryTimeoutError: http://riprova.readthedocs.io/en/latest/api.html#riprova.RetryTimeoutError .. _riprova.MaxRetriesExceeded: http://riprova.readthedocs.io/en/latest/api.html#riprova.MaxRetriesExceeded .. _riprova.NotRetriableError: http://riprova.readthedocs.io/en/latest/api.html#riprova.NotRetriableError

Examples ^^^^^^^^

You can see more featured examples from the documentation site.

Basic usage examples:

.. code-block:: python

import riprova

@riprova.retry
def task():
    """Retry operation if it fails with constant backoff (default)"""

@riprova.retry(backoff=riprova.ConstantBackoff(retries=5))
def task():
    """Retry operation if it fails with custom max number of retry attempts"""

@riprova.retry(backoff=riprova.ExponentialBackOff(factor=0.5))
def task():
    """Retry operation if it fails using exponential backoff"""

@riprova.retry(timeout=10)
def task():
    """Raises a TimeoutError if the retry loop exceeds from 10 seconds"""

def on_retry(err, next_try):
    print('Operation error: {}'.format(err))
    print('Next try in: {}ms'.format(next_try))

@riprova.retry(on_retry=on_retry)
def task():
    """Subscribe via function callback to every retry attempt"""

def evaluator(response):
    # Force retry operation if not a valid response
    if response.status >= 400:
        raise RuntimeError('invalid response status')  # or simple return True
    # Otherwise return False, meaning no retry
    return False

@riprova.retry(evaluator=evaluator)
def task():
    """Use a custom evaluator function to determine if the operation failed or not"""

@riprova.retry
async def task():
    """Asynchronous coroutines are also supported :)"""

Retry failed HTTP requests:

.. code-block:: python

import pook
import requests
from riprova import retry

# Define HTTP mocks to simulate failed requests
pook.get('server.com').times(3).reply(503)
pook.get('server.com').times(1).reply(200).json({'hello': 'world'})


# Retry evaluator function used to determine if the operated failed or not
def evaluator(response):
    if response != 200:
        return Exception('failed request')  # you can also simply return True
    return False


# On retry even subscriptor
def on_retry(err, next_try):
    print('Operation error {}'.format(err))
    print('Next try in {}ms'.format(next_try))


# Register retriable operation
@retry(evaluator=evaluator, on_retry=on_retry)
def fetch(url):
    return requests.get(url)


# Run task that might fail
fetch('http://server.com')

License

MIT - Tomas Aparicio

.. _exponential: https://en.wikipedia.org/wiki/Exponential_backoff .. _fibonacci: https://en.wikipedia.org/wiki/Fibonacci_number .. _asyncio: https://docs.python.org/3.5/library/asyncio.html .. _Python: http://python.org .. _annotated API reference: https://h2non.github.io/paco .. _async/await: https://www.python.org/dev/peps/pep-0492/ .. _yield from: https://www.python.org/dev/peps/pep-0380/ .. _documentation: http://riprova.readthedocs.io/en/latest/examples.html .. _read this article: http://dthain.blogspot.ie/2009/02/exponential-backoff-in-distributed.html .. _Constant backoff: http://riprova.readthedocs.io/en/latest/api.html#riprova.ConstantBackoff .. _Fibonacci backoff: http://riprova.readthedocs.io/en/latest/api.html#riprova.FibonacciBackoff .. _Exponential backoff: http://riprova.readthedocs.io/en/latest/api.html#riprova.ExponentialBackOff .. _ConstantBackoff: https://github.com/h2non/riprova/blob/master/riprova/strategies/constant.py .. _whitelisting: https://github.com/h2non/riprova/blob/master/examples/whitelisting_errors.py .. _blacklisting: https://github.com/h2non/riprova/blob/master/examples/blacklisting_errors.py .. _error evaluation: https://github.com/h2non/riprova/blob/master/examples/http_request.py .. _asynchronous coroutines: https://github.com/h2non/riprova/blob/master/examples/http_asyncio.py

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