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A comment on Memory use in CPython and MicroPython. Parent comment

Re:Memory use in CPython and MicroPython by ubernostrum on Sunday July 02, 2017 @05:42AM (#14681725)
When Python 3 broke compatibility, the Python team did exactly the thing you're supposed to do with code: first they made it correct (i.e., got all the changes implemented and working as expected), then made it fast.

"We're doing a huge rewrite already, let's pile on more scope" is a recipe for disaster.

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Re:Memory use in CPython and MicroPython by bonzini on Sunday July 02, 2017 @08:00AM (#14682118)
It depends. It is really surprising that Python does not use tagged integers, which is a 50 year old technique used by pretty much any other dynamic language in existence.

Using an extension API breakage as the excuse to introduce them would have made sense, since it also breaks the API. Now they cannot happen until Python 4.

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Re:Memory use in CPython and MicroPython by cdavid on Sunday July 02, 2017 @06:37PM (#14684698)
I believe ABC, one of python's influence, used tagged pointers, but I can't find a quote on this. Not using tagged pointers was a conscientious decision from Guido (see e.g. https://github.com/dropbox/pyston/issues/181#issuecomment-62...)

[edited] Something that people often overlook when talking about optimizing python is that the "simplicity" of the C Python API allowed the rich ecosystem of C extensions. GC, tagged pointers, etc... are great, and often used in modern VMs, but they tend to make integration w/ C code more difficult. Without rich C extensions, no numpy, no scipy, no scikit learn, no tensorflow/theano/etc... I am not sure this is completely incidental.

[edit 2] Ah, found the quote I remembered about tagged pointers in ABC from Guido: https://mail.python.org/pipermail/python-dev/2004-July/04614...

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Re:Memory use in CPython and MicroPython by netheril96 on Sunday July 02, 2017 @08:12AM (#14682145)
And Guido says he won't break backwards compat again in Python 4 as he has learned the lesson. No tagged integers for life.
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Re:Memory use in CPython and MicroPython by coldtea on Sunday July 02, 2017 @09:53AM (#14682492)
He learned the wrong lesson then. Which wasn't "don't break backwards compatibility", but:

1) If you break it, break it for compelling reasons.

2) If you provide a tool to convert, don't make it as awful as 2to3

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Re:Memory use in CPython and MicroPython by bonzini on Sunday July 02, 2017 @01:26PM (#14683407)
Breaking language backwards-compatibility is one thing; breaking the extension API is less problematic, and breaking the extension ABI is better still.
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