On Dec 15, 2:16 am, Steven D'Aprano <steve +comp.lang.pyt...@pearwood.info> wrote: > On Tue, 14 Dec 2010 21:14:35 +0000, kj wrote: > > Consider this code: > > > def spam(*args, **kwargs): > > args, kwargs = __pre_spam(*args, **kwargs) > > > # args & kwargs are OK: proceed > > # ... > > > def __pre_spam(*args, **kwargs): > > # validate args & kwargs; > > # return canonicalized versions of args & kwargs; # on failure, > > raise some *informative* exception # ... > > return canonicalized_args, canonicalized_kwargs > > Double leading underscores don't have any special meaning in the global > scope. Save yourself an underscore and call it _pre_spam instead :) > > In fact, even if spam and __pre_spam are methods, it's probably a good > idea to avoid the double-underscore name mangling. It's usually more > trouble than it's worth. > > > I write functions like __pre_spam for one reason only: to remove clutter > > from a corresponding spam function that has a particularly complex > > argument-validation/canonicalization stage. In effect, spam > > "outsources" to __pre_spam the messy business of checking and > > conditioning its arguments. > > A perfectly sensible arrangement. > > > The one thing I don't like about this strategy is that the tracebacks of > > exceptions raised during the execution of __pre_spam include one > > unwanted stack level (namely, the one corresponding to __pre_spam > > itself). > > But why is it unwanted? The traceback shows where the error occurs -- it > occurs in __pre_spam, not spam, or __post_spam, or spam_caller, or > anywhere else. Even if it's possible, having the traceback *lie* about > where it occurs is a bad idea which will cause confusion to anyone trying > to maintain the software in the future.
I don't agree with kj's usage, but I have customized the traceback to remove items before. In my case it was to remove lines for endemic wrapper functions. The traceback lines showing the wrapper functions in the stack were useless, and since pretty much every function was wrapped it meant half the lines in that traceback were useless. (Really. I was scanning the loaded modules and adding wrappers to every function found. Never mind why.) I only printed the wrapper line if it was the very top of the stack. > I can't think of any way to do it, You override sys.excepthook to print lines from the traceback selectively. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
