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| author | Nick Coghlan <ncoghlan@gmail.com> | 2006-04-23 16:05:04 (GMT) |
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| committer | Nick Coghlan <ncoghlan@gmail.com> | 2006-04-23 16:05:04 (GMT) |
| commit | e0ea50bc3b09e0f3b4f5fd3a531deeae94bcbb6d (patch) | |
| tree | 27e5927baf2c76425d19913cc5895e240b7371a0 /Doc/tut/tut.tex | |
| parent | fee3dfc061c4312636228aa48e0cf78a647645c9 (diff) | |
| download | cpython-e0ea50bc3b09e0f3b4f5fd3a531deeae94bcbb6d.zip cpython-e0ea50bc3b09e0f3b4f5fd3a531deeae94bcbb6d.tar.gz cpython-e0ea50bc3b09e0f3b4f5fd3a531deeae94bcbb6d.tar.bz2 | |
Add a (very) brief mention of the with statement to the end of chapter 8
Diffstat (limited to 'Doc/tut/tut.tex')
| -rw-r--r-- | Doc/tut/tut.tex | 36 |
1 files changed, 33 insertions, 3 deletions
diff --git a/Doc/tut/tut.tex b/Doc/tut/tut.tex index 78f5b1c..8df5510 100644 --- a/Doc/tut/tut.tex +++ b/Doc/tut/tut.tex @@ -941,9 +941,9 @@ with \function{str()}, conversion takes place using this default encoding. u'abc' >>> str(u"abc") 'abc' ->>> u"���" +>>> u"�" u'\xe4\xf6\xfc' ->>> str(u"���") +>>> str(u"�") Traceback (most recent call last): File "<stdin>", line 1, in ? UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-2: ordinal not in range(128) @@ -955,7 +955,7 @@ that takes one argument, the name of the encoding. Lowercase names for encodings are preferred. \begin{verbatim} ->>> u"���".encode('utf-8') +>>> u"�".encode('utf-8') '\xc3\xa4\xc3\xb6\xc3\xbc' \end{verbatim} @@ -3744,6 +3744,36 @@ In real world applications, the \keyword{finally} clause is useful for releasing external resources (such as files or network connections), regardless of whether the use of the resource was successful. +\section{Predefined Clean-up Actions \label{cleanup-with}} + +Some objects define standard clean-up actions to be undertaken when +the object is no longer needed, regardless of whether or not the +operation using the object succeeded or failed. +Look at the following example, which tries to open a file and print +its contents to the screen. + +\begin{verbatim} +for line in open("myfile.txt"): + print line +\end{verbatim} + +The problem with this code is that it leaves the file open for an +indeterminate amount of time after the code has finished executing. +This is not an issue in simple scripts, but can be a problem for +larger applications. The \keyword{with} statement allows +objects like files to be used in a way that ensures they are +always cleaned up promptly and correctly. + +\begin{verbatim} +with open("myfile.txt") as f: + for line in f: + print line +\end{verbatim} + +After the statement is executed, the file \var{f} is always closed, +even if a problem was encountered while processing the lines. Other +objects which provide predefined clean-up actions will indicate +this in their documentation. \chapter{Classes \label{classes}} |