<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Tue, Jan 27, 2015 at 8:20 AM, Guido van Rossum <span dir="ltr"><<a href="mailto:guido@python.org" target="_blank">guido@python.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><span class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div>A) Which test do we use:<br></div><div> 1) The asymmetric test<br></div><div> 2) The "strong" test (minimum relative tolerance)<br></div><div> 3) The "weak" test (maximum relative tolerance)<br clear="all"></div></div></div></div></blockquote><div><br></div></span><div>The problem with this question is that, while it's easy to come up with examples where it may matter (e.g. 95 is within 5% of 100, but 100 is not within %5 of 95), in practice the tolerance is more likely to be 1e-8, in which case it doesn't matter.<br></div></div></div></div></blockquote><div><br></div><div>Exactly why I'm happy with any of them. I'm trying to suss out whether anyone else has a reason to reject one or the others. If no one does, then we can just pick one.</div><div><br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><span class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div></div></div></div><div class="gmail_extra">B) Do we provide a non-zero default for the absolute tolerance? If so what should the value be? Remember that this serves primarily to provide a check against zero.<br></div></div></blockquote><div><br></div></span><div>It feels like absolute tolerance is a completely different test. And it is a much simpler test for which w don't need a helper function -- it's just abs(x) < tolerance.<br><br></div><div>When does a program need *both* absolute and relative tolerance in a single test?<br></div></div></div></div></blockquote><div><br></div><div>Because we want it to be able to do something sane when comparing to zero -- the abs_tolerance allows you to set a minimum tolerance that will do something reasonable near zero (we could use a zero_tolerance, as Nathaniel has suggested, instead, but that creates the incontinuity that , for example, 1e-12 is close to zero, but it is not close to 1e-100 -- I think that's a bad idea for a call with the same arguments). I spend a good while thinking about this and playing with it, and it became clear to me that this is the best way to go for a not-to-surprising result. And it's consistent with what numpy and Steven's statistics test code does.</div><div><br></div><div>Still TBD is what the default should be, though.</div><div> <br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><span class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"></div><div class="gmail_extra">I still think this is better off as a recipe than as a helper function.</div></div></blockquote></span></div></div></div></blockquote><div><br></div><div>Are you prepared to reject the PEP? I'd prefer to give it this one last shot at determining if there really is no way to get consensus on a good-enough solution. I suspect there is a lot of bike shedding here -- people have ideas about what is best, and want to understand and talk about it, but that doesn't mean that they wouldn't rather see something else that nothing. -- that's certainly the case for me (both the bike shedding and the desire to see something ;-) )</div><div><br></div><div>Evidence: The numpy version has its faults -- but it's widely used. assertAlmost Equal has even more faults (limitations, anyway) but it's also widely used. Boost has something in it, even though it's a one-liner. Clearly this is a useful functionality to have available.</div><div><br></div><div><br></div><div>ChrisA is right -- I have not done a good job at steering the group toward a consensus.</div><div><br></div><div>-Chris</div><div> </div></div><br clear="all"><div><br></div>-- <br><div class="gmail_signature"><br>Christopher Barker, Ph.D.<br>Oceanographer<br><br>Emergency Response Division<br>NOAA/NOS/OR&R (206) 526-6959 voice<br>7600 Sand Point Way NE (206) 526-6329 fax<br>Seattle, WA 98115 (206) 526-6317 main reception<br><br><a href="mailto:Chris.Barker@noaa.gov" target="_blank">Chris.Barker@noaa.gov</a></div>
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