[Python-ideas] list.sort with a int or str key (original) (raw)
Terry Reedy tjreedy at udel.edu
Fri Sep 17 05:11:22 CEST 2010
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On 9/16/2010 2:28 PM, Raymond Hettinger wrote:
The key= parameter is a protocol that is used across multiple tools min(). max(), groupby(), nmallest(), nlargest(), etc. All of those would need to change to stay in-sync. ...
ISTM, the performance would be about the same as you already get from attrgetter(), itemgetter(), and methodcaller(). Also, those three tools are already more flexible than the proposal, for example:
attrgetter('lastname', 'firstname') # key = lambda r: (r.lastname, r.firstname) itemgetter(0, 7) # key = lambda r: (r[0], r[7]) methodcaller('getstats', 'size') # key = lambda r: r.getstats('size')
It is easy to not know about these. I think the doc set could usefully use an expanded entry on key functions (that would be a cross-reference link) that includes examples like the above. Currently, for example, the min entry has "The optional keyword-only key argument specifies a one-argument ordering function like that used for list.sort()." but there is no link and going to list.sort only adds "that is used to extract a comparison key from each list element: key=str.lower. The default value is None." Perhaps we could expand that and make the existing cross-references into links.
-- Terry Jan Reedy
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