Hi All,
Apologies if you receive multiple copies of this, my python-announce posts don't seem to be making it through. I've just released a new python module called "withrestart". It's an attempted Pythonisation of the restart-based condition system of Common Lisp. Details are on PyPI: http://pypi.python.org/pypi/withrestart/0.2.1 For an introduction to conditions and restarts, see "Beyond Exception Handling" by Peter Seibel: http://www.gigamonkeys.com/book/beyond-exception-handling-conditions-and-restarts.html For a quick demo of the module in action, keep reading... Cheers, Ryan About withrestart: ------------------ Version: 0.2.1 Licence: MIT Source: http://github.com/rfk/withrestart withrestart is a Pythonisation (Lispers might rightly say "bastardisation") of the restart-based condition system of Common Lisp. It's designed to make error recovery simpler and easier by removing the assumption that unhandled errors must be fatal. A "restart" represents a named strategy for resuming execution of a function after the occurrence of an error. At any point during its execution a function can push a Restart object onto its call stack. If an exception occurs within the scope of that Restart, code higher-up in the call chain can invoke it to recover from the error and let the function continue execution. By providing several restarts, functions can offer several different strategies for recovering from errors. A "handler" represents a higher-level strategy for dealing with the occurrence of an error. It is conceptually similar to an "except" clause, in that one establishes a suite of Handler objects to be invoked if an error occurs during the execution of some code. There is, however, a crucial difference: handlers are executed without unwinding the call stack. They thus have the opportunity to take corrective action and then resume execution of whatever function raised the error. As an example, here's a function that doesn't like the number seven: def anything_but_seven(v): if v == 7: raise ValueError("Argh! A Seven!") return v And here's a function that can recover from the occurrence of a seven using the pre-defined restarts "skip" and "use_value": def sum_items(items): total = 0 for i in items: with restarts(skip,use_value) as invoke: total += invoke(anything_but_seven,i) return total Naively calling this will raise a ValueError: >>> sum_items(range(8)) Traceback (most recent call last): ... ValueError: Argh! A Seven! >>> But if we handle ValueErrors by invoking the "skip" restart, we can still get the sum of the remaining items: >>> with Handler(ValueError,"skip"): ... sum_items(range(8)) ... 21 >>> Alternately, we can invoke the "use_value" restart to replace the sevens with another value: >>> with Handler(ValueError,"use_value",12): ... sum_items(range(8)) ... 33 >>> By splitting the responsibility for error recovery between Handlers and Restarts, we can cleanly separate the low-level mechanics of recovering from an error from the high-level decisions about what sort of recovery to perform. -- Ryan Kelly http://www.rfk.id.au | This message is digitally signed. Please visit r...@rfk.id.au | http://www.rfk.id.au/ramblings/gpg/ for details
signature.asc
Description: This is a digitally signed message part
-- http://mail.python.org/mailman/listinfo/python-list