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operator.itemgetter() and operator.attrgetter() now support extraction

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of multiple fields.  This provides direct support for sorting by
multiple keys.
This commit is contained in:
Raymond Hettinger 2005-03-09 16:38:48 +00:00
parent 6a3f4f7bc3
commit 984f9bb714
4 changed files with 118 additions and 23 deletions
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15
Doc/lib/liboperator.tex
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@ -306,24 +306,31 @@ as arguments for \function{map()}, \function{sorted()},
\method{itertools.groupby()}, or other functions that expect a
function argument.
\begin{funcdesc}{attrgetter}{attr}
\begin{funcdesc}{attrgetter}{attr\optional{, args...}}
Return a callable object that fetches \var{attr} from its operand.
If more than one attribute is requested, returns a tuple of attributes.
After, \samp{f=attrgetter('name')}, the call \samp{f(b)} returns
\samp{b.name}.
\samp{b.name}. After, \samp{f=attrgetter('name', 'date')}, the call
\samp{f(b)} returns \samp{(b.name, b.date)}.
\versionadded{2.4}
\versionchanged[Added support for multiple attributes]{2.5}
\end{funcdesc}
\begin{funcdesc}{itemgetter}{item}
\begin{funcdesc}{itemgetter}{item\optional{, args...}}
Return a callable object that fetches \var{item} from its operand.
If more than one item is requested, returns a tuple of items.
After, \samp{f=itemgetter(2)}, the call \samp{f(b)} returns
\samp{b[2]}.
After, \samp{f=itemgetter(2,5,3)}, the call \samp{f(b)} returns
\samp{(b[2], b[5], b[3])}.
\versionadded{2.4}
\versionchanged[Added support for multiple item extraction]{2.5}
\end{funcdesc}
Examples:
\begin{verbatim}
>>> from operator import *
>>> from operator import itemgetter
>>> inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)]
>>> getcount = itemgetter(1)
>>> map(getcount, inventory)