I think you are looking for __nonzero__ and __bool__ and the evaluation of them is different between versions of python. A quick google search doesnt show anything promising but those are the interfaces I think.<div><br><br>
<div class="gmail_quote">On Fri, Mar 19, 2010 at 9:54 AM, Jonathan Hayward <span dir="ltr"><<a href="mailto:christos.jonathan.hayward@gmail.com">christos.jonathan.hayward@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
There was something I thought I'd read but couldn't track down in the documentation.<div><br></div><div>User-defined classes normally evaluate to true, i.e. if you define:</div><div><br></div><div>class foo:</div>
<div>
pass</div><div><br></div><div>bar = foo()</div><div><br></div><div>if bar:</div><div> print "True"</div><div>else:</div><div> print "False"</div><div><br></div><div>then the output will be "True", and adding real functionality to foo does not change this.</div>
<div><br></div><div>I thought there was supposed to be a method you could define that would override this behavior, named something like is_true() or __is_true__(), so that an object could be set to evaluate to false. However, looking through the documentation did not confirm anything like:</div>
<div><br></div><div>class foo:</div><div> def is_true(self):</div><div> return False</div><div><br></div><div>bar = foo()</div><div><br></div><div>if bar:</div><div> print "True"</div><div>else:</div>
<div> print "False"</div><div><br></div><div>which would print "False".</div><div><br></div><div>Is there such a method that can be defined, or is it non-negotiable that a user-defined class (which does not extend a class that can be falsy) will evaluate to true?</div>
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