[Python-3000] BLists (PEP 3128) (original) (raw)

Daniel Stutzbach daniel at stutzbachenterprises.com
Mon May 28 21:41:44 CEST 2007

On 5/11/07, Raymond Hettinger <python at rcn.com> wrote:

> Would it be useful if I created an experimental fork of 2.5 > that replaces array-based lists with BLists, > so that the performance penalty (if any) on existing code > can be measured?

That would likely be an informative exercise and would assure that your code is truly interchangable with regular lists. It would also highlight the under-the-hood difficulties you'll encounter with the C-API. That being said, it is a labor intensive exercise and the time might be better spent on tweaking the third-party module code and building a happy user-base.

Just to provide a quick update on my adventures with BLists:

I went forward with the exercise of replacing the array-based list with BLists in the Python interpreter. As a first pass, I went with a simple, not-very-efficient redirect of the List API. I had very few problems getting this working well enough to compile.

The exercise also had the benefit that I have been able to test BLists against the entire Python test suite. Previously, I had adapted only test_list. test_builtin was particularly useful. I was able to find and fix a couple more bugs in my implementation this way. Almost all of the tests pass now.

There are also a handful of test failures where the tests are asserting the CPython implementation details when the intent is really just to assert(don't crash). These tests are related to when references are deleted to evil comparison/lookup functions or what happens when a list changes size during iteration. I'll probably change the BList code to match CPython's behavior.

I have one genuine bug to fix that inexplicably causes test_shlex to fail. Once that is taken care of, I get back to looking at performance.

However, I'm leaving tomorrow for 3 weeks (wedding + honeymoon), so I'm not going to be able to make any further progress until I get back. :-)

-- Daniel Stutzbach, Ph.D. President, Stutzbach Enterprises LLC

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