Richard Lewis schreef: > Is it possible to have an 'except' case which passes control back to the > point after the exception occurred?
No, not in Python. The concept has however been discussed, under the name "resumable exceptions". http://www.google.com/search?num=100&q=%22resumable+exceptions%22+site%3Apython.org An excellent article about the concept was written by Kent Pitman: "Condition Handling in the Lisp Language Family" http://www.nhplace.com/kent/Papers/Condition-Handling-2001.html Common Lisp is a language that does have the feature. Your code would be written in Lisp like below. When the function notices the file is locked, it will raise an exception. Now imagine there are two ways to solve the problem: 1) read the file anyway, despite the lock; 2) clear the lock and read the file. Or reading the file could be cancelled. These three possible ways to continue the execution are set up by "restart-case". (So this is actually a generalization of your request, in that instead of "just continueing", you can direct the way of continuing) (defun read-unlocked-file (file-name) (with-open-file (f file-name) (when (string= (read-line f) "FILE LOCKED") (let ((user "lock-user") (timestamp 123)) (restart-case (error 'file-locked :name file-name :user user :timestamp timestamp) (continue () :report "Continue reading the locked file.") (clear-lock () :report "Clear the lock and continue reading" (warn "clearing lock...")) (abort () :report "Abort reading the file." (return-from read-unlocked-file))))) (warn "reading remainder of file...") t)) When reading a locked file, you end up with this message: CL-USER(31): (read-unlocked-file "file.txt") Error: File file.txt was locked by lock-user at time 123. [condition type: FILE-LOCKED] Restart actions (select using :continue): 0: Continue reading the locked file. 1: Clear the lock and continue reading 2: Abort reading the file. 3: Return to Top Level (an "abort" restart). 4: Abort entirely from this process. Note the three first "restart actions" are the ones we just defined inside "read-unlocked-file". Let's continue execution by clearing the lock (restart number 1): [1] CL-USER(32): :continue 1 Warning: clearing lock... Warning: reading remainder of file... T If Python had restarts, in your example you would set up code that, depending on whether the user clicked "abort" or "continue" in the dialog, automatically invokes the corresponding restart to either continue or abort the calculation. Restarts are pretty cool. Maybe Stackless Python could support it fairly easily, restarts basically being named continuations? - Willem -- http://mail.python.org/mailman/listinfo/python-list
