82 lines
2.2 KiB
Plaintext
82 lines
2.2 KiB
Plaintext
PEP: 270
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Title: uniq method for list objects
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Author: Jason Petrone <jp@demonseed.net>
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Status: Rejected
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Type: Standards Track
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Content-Type: text/x-rst
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Created: 21-Aug-2001
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Python-Version: 2.2
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Post-History:
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Notice
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======
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This PEP is withdrawn by the author. He writes:
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Removing duplicate elements from a list is a common task, but
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there are only two reasons I can see for making it a built-in.
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The first is if it could be done much faster, which isn't the
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case. The second is if it makes it significantly easier to
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write code. The introduction of ``sets.py`` eliminates this
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situation since creating a sequence without duplicates is just
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a matter of choosing a different data structure: a set instead
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of a list.
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As described in :pep:`218`, sets are being added to the standard
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library for Python 2.3.
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Abstract
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========
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This PEP proposes adding a method for removing duplicate elements to
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the list object.
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Rationale
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=========
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Removing duplicates from a list is a common task. I think it is
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useful and general enough to belong as a method in list objects.
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It also has potential for faster execution when implemented in C,
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especially if optimization using hashing or sorted cannot be used.
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On comp.lang.python there are many, many, posts [1]_ asking about
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the best way to do this task. It's a little tricky to implement
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optimally and it would be nice to save people the trouble of
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figuring it out themselves.
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Considerations
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==============
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Tim Peters suggests trying to use a hash table, then trying to
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sort, and finally falling back on brute force [2]_. Should uniq
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maintain list order at the expense of speed?
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Is it spelled 'uniq' or 'unique'?
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Reference Implementation
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========================
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I've written the brute force version. It's about 20 lines of code
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in ``listobject.c``. Adding support for hash table and sorted
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duplicate removal would only take another hour or so.
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References
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==========
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.. [1] https://groups.google.com/forum/#!searchin/comp.lang.python/duplicates
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.. [2] Tim Peters unique() entry in the Python cookbook:
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http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52560/index_txt
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Copyright
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=========
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This document has been placed in the public domain.
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