<div dir="auto">Can you show some sample code that you have written that shows where this would be useful?<div dir="auto"><br></div><div dir="auto">Note that using the numbers package actually makes static type checking through e.g. mypy difficult. So I presume you are talking about dynamic checking?</div><div dir="auto"><br></div><div dir="auto">--Guido</div><br><div class="gmail_extra" dir="auto"><br><div class="gmail_quote">On Feb 14, 2018 12:42 AM, "Sylvain MARIE" <<a href="mailto:sylvain.marie@schneider-electric.com">sylvain.marie@schneider-electric.com</a>> wrote:<br type="attribution"><blockquote class="quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">My point is just that today, I use the ‘numbers’ package classes (Integral, Real, …) for PEP484 type-hinting, and I find it quite useful
in term of input type validation (in combination with PEP484-compliant type checkers, whether static or dynamic). Adding a Boolean ABC with a similar behavior would certainly add consistency to that ‘numbers’ package – only for users who already find it useful,
of course.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">Note that my use case is not about converting an object to a Boolean, I’m just speaking about type validation of a ‘true’ boolean object,
for example to be received as a function argument for a flag option. This is for example for users who want to define strongly-typed APIs for interaction with the ‘outside world’, and keep using duck-typing for internals.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial",sans-serif">Sylvain
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"><u></u><u></u></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">De :</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Python-ideas [mailto:<a href="mailto:python-ideas-bounces%2Bsylvain.marie" target="_blank">python-ideas-bounces+<wbr>sylvain.marie</a>=<a href="mailto:schneider-electric.com@python.org" target="_blank">schneider-<wbr>electric.com@python.org</a>]
<b>De la part de</b> Chris Barker<br>
<b>Envoyé :</b> mardi 13 février 2018 21:12<br>
<b>À :</b> David Mertz <<a href="mailto:mertz@gnosis.cx" target="_blank">mertz@gnosis.cx</a>><br>
<b>Cc :</b> python-ideas <<a href="mailto:python-ideas@python.org" target="_blank">python-ideas@python.org</a>><br>
<b>Objet :</b> Re: [Python-ideas] Boolean ABC similar to what's provided in the 'numbers' module<u></u><u></u></span></p><div class="elided-text">
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">On Mon, Feb 12, 2018 at 10:07 PM, David Mertz <</span><a href="mailto:mertz@gnosis.cx" target="_blank"><span lang="EN-US">mertz@gnosis.cx</span></a><span lang="EN-US">> wrote:<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">I'm not sure I'm convinced by Sylvain that Boolean needs to be an ABC in the standard library; Guido expresses skepticism. Of course it is possible to define it in some other library that actually needs to use `isinstance(x,
Boolean)` as Sylvain demonstraits in his post. I'm not sure I'm unconvinced either, I can see a certain value to saying a given value is "fully round-trippable to bool" (as is np.bool_).<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">But is an ABC the way to do it? Personally, I'm skeptical that ABCs are a solution to, well, anything (as apposed to duck typing and EAFTP). Take Nick's example:<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:9.5pt">"""</span><span lang="EN-US"><u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:9.5pt">The other comparison that comes to mind would be the distinction<br>
between "__int__" ("can be coerced to an integer, but may lose<br>
information in the process") and "__index__" ("can be losslessly<br>
converted to and from a builtin integer").</span><span lang="EN-US"><u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">""" <u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">I suppose we could have had an Index ABC -- but that seems painful to me.<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">so maybe we could use a __true_bool__ special method? <u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">(and an operator.true_bool() function ???)<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">(this all makes me wish that python bools were more pure -- but way to late for that!)<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">I guess it comes down to whether you want to:<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"> - Ask the question: "is this object a boolean?"<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">or<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"> - Make this object a boolean<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">__index__ (and operator.index()) is essentially the later -- you want to make an index out of whatever object you have, if you can do so.<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">-CHB<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US">-- <u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US"><br>
Christopher Barker, Ph.D.<br>
Oceanographer<br>
<br>
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<br>
</span><a href="mailto:Chris.Barker@noaa.gov" target="_blank"><span lang="EN-US">Chris.Barker@noaa.gov</span></a><span lang="EN-US"><u></u><u></u></span></p>
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