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SF patch #980695: efficient string concatenation

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(Original patch by Armin Rigo).
This commit is contained in:
Raymond Hettinger 2004-08-06 18:43:09 +00:00
parent d09d9664e6
commit 52a21b8e65
3 changed files with 107 additions and 3 deletions
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12
Doc/lib/libstdtypes.tex
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@ -455,7 +455,7 @@ and \var{j} are integers:
\lineiii{\var{x} not in \var{s}}{\code{0} if an item of \var{s} is
equal to \var{x}, else \code{1}}{(1)}
\hline
\lineiii{\var{s} + \var{t}}{the concatenation of \var{s} and \var{t}}{}
\lineiii{\var{s} + \var{t}}{the concatenation of \var{s} and \var{t}}{(6)}
\lineiii{\var{s} * \var{n}\textrm{,} \var{n} * \var{s}}{\var{n} shallow copies of \var{s} concatenated}{(2)}
\hline
\lineiii{\var{s}[\var{i}]}{\var{i}'th item of \var{s}, origin 0}{(3)}
@ -536,6 +536,16 @@ In Python 2.3 and beyond, \var{x} may be a string of any length.
(which end depends on the sign of \var{k}). Note, \var{k} cannot
be zero.
\item[(6)] If \var{s} and \var{t} are both strings, some Python
implementations such as CPython can usally perform an inplace optimization
for assignments of the form \code{\var{s}=\var{s}+\var{t}} or
\code{\var{s}+=\var{t}}. When applicable, this optimization makes
quadratic run-time much less likely. This optimization is both version
and implementation dependent. For performance sensitive code, it is
preferrable to use the \method{str.join()} method which assures consistent
linear concatenation performance across versions and implementations.
\versionchanged[Formerly, string concatenation never occurred inplace]{2.4}
\end{description}