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| This PEP is withdrawn by the author.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