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| -rw-r--r-- | Doc/whatsnew/whatsnew24.tex | 38 |
1 files changed, 37 insertions, 1 deletions
diff --git a/Doc/whatsnew/whatsnew24.tex b/Doc/whatsnew/whatsnew24.tex index 5fda620..efa1ef2 100644 --- a/Doc/whatsnew/whatsnew24.tex +++ b/Doc/whatsnew/whatsnew24.tex @@ -38,7 +38,43 @@ Here are all of the changes that Python 2.4 makes to the core Python language. \begin{itemize} -\item TBD +\item The \method{sort()} method of lists gained three keyword +arguments, \var{cmp}, \var{key}, and \var{reverse}. These arguments +make some common usages of \method{sort()} simpler. All are optional. + +\var{cmp} is the same as the previous single argument to +\method{sort()}; if provided, the value should be a comparison +function that takes two arguments and returns -1, 0, or +1 depending +on how the arguments compare. + +\var{key} should be a single-argument function that takes a list +element and returns a comparison key for the element. The list is +then sorted using the comparison keys. The following example sorts a list +case-insensitively: + +\begin{verbatim} +>>> L = ['A', 'b', 'c', 'D'] +>>> L.sort() # Case-sensitive sort +>>> L +['A', 'D', 'b', 'c'] +>>> L.sort(key=lambda x: x.lower()) +>>> L +['A', 'b', 'c', 'D'] +>>> L.sort(cmp=lambda x,y: cmp(x.lower(), y.lower())) +>>> L +['A', 'b', 'c', 'D'] +\end{verbatim} + +The last example, which uses the \var{cmp} parameter, is the old way +to perform a case-insensitive sort. It works, but is slower than +using a \var{key} parameter. Using \var{key} results in calling the +\method{lower()} method once for each element in the list while using +\var{cmp} will call the method twice for each comparison. + +The \var{reverse} parameter should have a Boolean value. If the value is +\constant{True}, the list will be sorted into reverse order. Instead +of \code{L.sort() ; L.reverse()}, you can now write +\code{L.sort(reverse=True)}. \end{itemize} |