<div dir="ltr">But neither UserDict nor MutableMapping defines __missing__ ?  What is a subclasser supposed to do? On Wednesday, June 29, 2016 at 4:59:03 PM UTC-4, Guido van Rossum wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;">UserDict is superseded by MutableMapping.

<br>

<br>I don't think we should make dict a kitchen sink class. I also don't

<br>think we should particularly encourage subclassing it. So -1 on adding

dict.__missing__.

<br>

<br>On Wed, Jun 29, 2016 at 12:30 PM, Ethan Furman <<a href="javascript:" target="_blank" gdf-obfuscated-mailto="KX7BhAw6CwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">et...@stoneleaf.us</a>> wrote:

<br>> On 06/29/2016 12:09 PM, Guido van Rossum wrote:

<br>>

<br>>> So providing the comprehensive base class is up to the user, not up to

>> the stdlib. Is that such a big deal?

<br>>

<br>>

<br>> No, it's not.  But it makes for a better user experience if the base class

> has the __missing__ method that raises a KeyError already.

<br>>

<br>> Didn't we add a UserDict that could be subclassed primarily because

> subclassing dict directly was such a poor user experience?

<br>>

> If adding __missing__ to dict is huge (performance hit?), we don't do it.

<br>> If it's not, I think we should.  Maybe add it to UserDict if performance is

<br>> a concern?

<br>>

<br>>

<br>> --

<br>> ~Ethan~

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<br>

<br>

<br>

<br>-- 

<br>--Guido van Rossum (<a href="http://python.org/~guido" target="_blank" rel="nofollow" onmousedown="this.href='http://www.google.com/url?q\x3dhttp%3A%2F%2Fpython.org%2F~guido\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNGKI5lSgzXFUM7Y5HtkFAp6sQAxEg';return true;" onclick="this.href='http://www.google.com/url?q\x3dhttp%3A%2F%2Fpython.org%2F~guido\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNGKI5lSgzXFUM7Y5HtkFAp6sQAxEg';return true;">python.org/~guido</a>)

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