<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><span></span></div><div><meta http-equiv="content-type" content="text/html; charset=utf-8"><div></div><div><blockquote type="cite"><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">On Fri, Apr 08, 2016 at 11:24:15AM -0700, <a href="mailto:rian@thelig.ht">rian@thelig.ht</a> wrote:<br></span></font></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">I want to live in a world where I can do this:<br></span></font></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"> while cbs:<br></span></font></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"> cb = cbs.pop()<br></span></font></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"> try:<br></span></font></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"> cb()<br></span></font></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"> except Exception as e:<br></span></font></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"> logging.exception("In main loop")<br></span></font></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"> if is_a_bug(e):<br></span></font></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"> raise SystemExit() from e<br></span></font></blockquote></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">And I want a pony :-)<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">So long as Python allows people to write code like this:<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"># A deliberately silly example<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">if len(seq) == 0:<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"> raise ImportError("assertion fails")<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">you cannot expect to automatically know what an exception means without <br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">any context of where it came from and why it happened. The above example <br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">is silly, but it doesn't take much effort to come up with more serious <br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">ones:<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">- an interpreter written in Python may raise SyntaxError, which <br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">is not a bug in the interpreter;<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">- a test framework may raise AssertionError for a failed test,<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">which is not a bug in the framework;<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">- a function may raise MemoryError if the call *would* run out of<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">memory, but without actually running out of memory; consequently<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">it is not a fatal error, while another function may raise the <br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">same MemoryError because it actually did fatally run out of memory.<br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">Effectively, you want the compiler to Do What I Mean when it comes to <br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">exceptions. DWIM may, occasionally, be a good idea in applications, but <br></span></font></blockquote><blockquote type="cite"><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">I maintain it is never a good idea in a programming language. <br></span></font></blockquote><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br>I think you're misinterpreting me. I don't want a pony and I don't want a sufficiently smart compiler.<br><br>I want a consistent opt-in idiom with community consensus. I want a clear way to express that an exception is an error and not an internal bug. It doesn't have to catch 100% of cases, the idiom just needs to approach consistency across all Python libraries that I may import.</span></font></div><div><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></div><div><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">If the programmer doesn't pay attention to the idiom, then is_a_bug() will never return true (or not True if it's is_not_a_bug()). AssertionError is already unambiguous, I'm sure there are other candidates as well.</span></font></div><div><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></div><div><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">I'm not the first or only one to want something like this <a href="http://blog.tsunanet.net/2012/10/pythons-screwed-up-exception-hierarchy.html">http://blog.tsunanet.net/2012/10/pythons-screwed-up-exception-hierarchy.html</a></span></font></div><div><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></font></div><div><font color="#000000"><span style="background-color: rgba(255, 255, 255, 0);">But I can see the pile on has begun and my point is lost. Maybe this will get added in ten or twenty years.</span></font></div></div></body></html>