But our expectation about temporary nature of service behavior will never happen. Service sometimes work slowly, sometimes return HTTP errors and so on. We receive tons of exceptions every day. We had to do something with that.
The solution: Here is safe_exec decorator which help solve this problem. You can specify how many times you want to try execute function, what's timeout between them and what exceptions are expected during execution decorated function. For example, urllib2.urlopen may generate urllib2.URLError or urllib2.HTTPError.
import logging import time from functools import wraps __all__ = ("safe_exec",) def safe_exec(exceptions, shakes=3, timeout=1, title="", **kwargs): """ Decorator to safely execute function or method within `shakes` trying. In case provide argument `default` exception will not be raised and will return provided value. """ def wrap(func): if not isinstance(exceptions, tuple): raise TypeError( "First argument of safe_exec should be tuple of exceptions" ) @wraps(func) def wrapped(*args, **kwargs): result = None orig_exception = None for shake in range(shakes): try: result = func(*args, **kwargs) break except exceptions, orig_exception: logging.warn("%s: Sorry, can't execute %s, shake #%d", title, func.__name__, shake, exc_info=True ) time.sleep(timeout) else: logging.error( "%s: Can't execute `%s` after %d shakes", title, func.__name__, shakes ) if "default" in kwargs: return kwargs.get("default") raise orig_exception return result return wrapped return wrap
import urllib2 @safe_exec((urllib2.URLError, urllib2.HTTPError), shakes=2) def download(url): return urllib2.urlopen(url).read() download("http://slow-resource.com/")