Top-rated recipes tagged "reraise" Code RecipesPython Exception Chains (or Trees) (Python) 2013-02-04T15:15:22-08:00Alfe <p style="color: grey"> Python recipe 578252 by <a href="/recipes/users/4182236/">Alfe</a> (<a href="/recipes/tags/cause/">cause</a>, <a href="/recipes/tags/chain/">chain</a>, <a href="/recipes/tags/exception/">exception</a>, <a href="/recipes/tags/python/">python</a>, <a href="/recipes/tags/reason/">reason</a>, <a href="/recipes/tags/reraise/">reraise</a>, <a href="/recipes/tags/tree/">tree</a>). Revision 2. </p> <p>I have here an approach for chaining exceptions in case a lower layer (<em>library</em>) raises an exception which is caught in an upper layer (<em>application</em>) and later given as <em>cause</em> when a different exception is raised. Passing this <em>cause</em> exception is meant to offer access to the stack trace of the inner exception for debugging.</p> <p>This approach is implemented in Python 3 and in Java, so it definitely makes sense; you also quickly find questions on <a href="">Stackoverflow</a> concerning it.</p> <p>I even extended this feature by not only using chains of exceptions but also trees. Trees, why trees? Because I had situations in which my application layer tried various approaches using the library layer. If all failed (raised an exception), my application layer also raised an exception; this is the case in which I wanted to pass more than one cause exception into my own exception (hence the tree of causes).</p> <p>My approach uses a special Exception class from which all my exceptions will inherit; standard exception must be wrapped (directly after catching, to preserve the exception stack trace). Please see the examples contained in the code below. The exception itself is rather small.</p> <p>I'd be happy to hear any comments regarding memory leaks (I didn't find any but one never knows), usability, enhancements or similar.</p>