Ignore all real exceptions (descendants of Exception). Handy for cleaning data such as user input:

brand_id = silent(int)(request.GET['brand_id'])
ids = keep(silent(int), request.GET.getlist('id'))

And in data import/transform:

get_greeting = compose(silent(string.lower), re_finder(r'(\w+)!'))
map(get_greeting, ['a!', ' B!', 'c.'])
# -> ['a', 'b', None]


Avoid silencing non-primitive functions, use ignore() instead and even then be careful not to swallow exceptions unintentionally.

@ignore(errors, default=None)

Same as silent(), but able to specify errors to catch and default to return in case of error caught. errors can either be exception class or tuple of them.

raiser(exception_or_class=Exception, *args, **kwargs)

Constructs function that raises given exception with given arguments on any invocation.

@retry(tries, errors=Exception)

Every call of decorated function retried up to tries times if any subclass of errors occurs (could be exception class or a tuple of them).


Tries several approaches until one works. Each approach is either callable or a tuple (callable, errors), where errors is an exception class or a tuple of classes, which signal to fall back to next approach. If errors is not supplied then fall back is done for any Exception:

    (partial(send_mail, ADMIN_EMAIL, message), SMTPException),
    partial(log.error, message),
    raiser(FeedbackError, "Unable to notify admin")
limit_error_rate(fails, timeout, exception=ErrorRateExceeded)

If function fails to complete fails times in a row, calls to it will be intercepted for timeout with exception raised instead. A clean way to short-circuit function taking too long to fail:

@limit_error_rate(fails=5, timeout=60, exception=RequestError('Temporary unavailable'))
def do_request(query):
    # ... make a http request
    return data

Transforms generator or other iterator returning function into list returning one.

Handy to prevent quirky iterator-returning properties:

def path_up(self):
    node = self
    while node:
        yield node
        node = node.parent

Also makes list constructing functions beautifully yielding.


Wraps common python idiom “collect then join” into a decorator. Transforms generator or alike into function, returning string of joined results. Automatically converts all elements to separator type for convenience.

Goes well with generators with some ad-hoc logic within:

@joining(', ')
def car_desc(self):
    yield self.year_made
    if self.engine_volume: yield '%s cc' % self.engine_volume
    if self.transmission:  yield self.get_transmission_display()
    if self.gear:          yield self.get_gear_display()
    # ...

Use unicode separator to get unicode result:

@joining(u', ')
def car_desc(self):
    yield self.year_made
    # ...

See also str_join().