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\section{\module{xreadlines} ---
Efficient iteration over a file}
\declaremodule{extension}{xreadlines}
\modulesynopsis{Efficient iteration over the lines of a file.}
\versionadded{2.1}
This module defines a new object type which can efficiently iterate
over the lines of a file. An xreadlines object is a sequence type
which implements simple in-order indexing beginning at \code{0}, as
required by \keyword{for} statement or the
\function{filter()} function.
Thus, the code
\begin{verbatim}
import xreadlines, sys
for line in xreadlines.xreadlines(sys.stdin):
pass
\end{verbatim}
has approximately the same speed and memory consumption as
\begin{verbatim}
while 1:
lines = sys.stdin.readlines(8*1024)
if not lines: break
for line in lines:
pass
\end{verbatim}
except the clarity of the \keyword{for} statement is retained in the
former case.
\begin{funcdesc}{xreadlines}{fileobj}
Return a new xreadlines object which will iterate over the contents
of \var{fileobj}. \var{fileobj} must have a \method{readlines()}
method that supports the \var{sizehint} parameter. \note{Because
the \method{readlines()} method buffers data, this effectively
ignores the effects of setting the file object as unbuffered.}
\end{funcdesc}
An xreadlines object \var{s} supports the following sequence
operation:
\begin{tableii}{c|l}{code}{Operation}{Result}
\lineii{\var{s}[\var{i}]}{\var{i}'th line of \var{s}}
\end{tableii}
If successive values of \var{i} are not sequential starting from
\code{0}, this code will raise \exception{RuntimeError}.
After the last line of the file is read, this code will raise an
\exception{IndexError}.
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