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<b class="current">File handles</b>
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<div><h1 id="a0000000055">6.9 File handles</h1>
<p>File handles provide a means of reading data directly from text files, or of writing data or logging information to files. Files are opened using the <tt class="tt">open()</tt> function: </p><p> <big class="large"><b class="bf">open(<img src="images/img-0030.png" alt="$x$" style="vertical-align:0px;
width:10px;
height:8px" class="math gen" />[,<img src="images/img-0031.png" alt="$y$" style="vertical-align:-4px;
width:9px;
height:12px" class="math gen" />])</b></big> <br />The open(<img src="images/img-0030.png" alt="$x$" style="vertical-align:0px;
width:10px;
height:8px" class="math gen" />[,<img src="images/img-0031.png" alt="$y$" style="vertical-align:-4px;
width:9px;
height:12px" class="math gen" />]) function opens the file <img src="images/img-0030.png" alt="$x$" style="vertical-align:0px;
width:10px;
height:8px" class="math gen" /> with string access mode <img src="images/img-0031.png" alt="$y$" style="vertical-align:-4px;
width:9px;
height:12px" class="math gen" />, and returns a file handle object. <a name="a0000000639" id="a0000000639"></a> </p><p>The most commonly used access modes are <tt class="tt">"r"</tt>, to open a file read-only, <tt class="tt">"w"</tt>, to open a file for writing, erasing any pre-existing file of the same filename, and <tt class="tt">"a"</tt>, to append data to the end of a file. </p><p>Alternatively, if what is wanted is a temporary scratch space, the <tt class="tt">os.tmpfile()</tt> function should be used: </p><p> <big class="large"><b class="bf">os.tmpfile()</b></big> <br />The os.tmpfile() function returns a file handle for a temporary file. The resulting file handle is open for both reading and writing. <a name="a0000000640" id="a0000000640"></a> </p><p>The following methods are defined for file handles: </p><p> <big class="large"><b class="bf">close()</b></big> <br />The close() method closes a file handle. <a name="a0000000641" id="a0000000641"></a> </p><p> <big class="large"><b class="bf">dump(<img src="images/img-0030.png" alt="$x$" style="vertical-align:0px;
width:10px;
height:8px" class="math gen" />)</b></big> <br />The dump(<img src="images/img-0030.png" alt="$x$" style="vertical-align:0px;
width:10px;
height:8px" class="math gen" />) method stores a typeable ASCII representation of the object <img src="images/img-0030.png" alt="$x$" style="vertical-align:0px;
width:10px;
height:8px" class="math gen" /> to a file. Note that this method has no checking for recursive hierarchical data structures. <a name="a0000000642" id="a0000000642"></a> </p><p> <big class="large"><b class="bf">eof()</b></big> <br />The eof() method returns a boolean flag to indicate whether the end of a file has been reached. <a name="a0000000643" id="a0000000643"></a> </p><p> <big class="large"><b class="bf">flush()</b></big> <br />The flush() method flushes any buffered data which has not yet physically been written to a file. <a name="a0000000644" id="a0000000644"></a> </p><p> <big class="large"><b class="bf">getPos()</b></big> <br />The getPos() method returns a file handle’s current position in a file. <a name="a0000000645" id="a0000000645"></a> </p><p> <big class="large"><b class="bf">isOpen()</b></big> <br />The isOpen() method returns a boolean flag indicating whether a file is open. <a name="a0000000646" id="a0000000646"></a> </p><p> <big class="large"><b class="bf">read()</b></big> <br />The read() method returns the contents of a file as a string. <a name="a0000000647" id="a0000000647"></a> </p><p> <big class="large"><b class="bf">readline()</b></big> <br />The readline() method returns a single line of a file as a string. <a name="a0000000648" id="a0000000648"></a> </p><p> <big class="large"><b class="bf">readlines()</b></big> <br />The readlines() method returns the lines of a file as a list of strings. <a name="a0000000649" id="a0000000649"></a> </p><p> <big class="large"><b class="bf">setPos(<img src="images/img-0030.png" alt="$x$" style="vertical-align:0px;
width:10px;
height:8px" class="math gen" />)</b></big> <br />The setPos(<img src="images/img-0030.png" alt="$x$" style="vertical-align:0px;
width:10px;
height:8px" class="math gen" />) method sets a file handle’s current position in a file. <a name="a0000000650" id="a0000000650"></a> </p><p> <big class="large"><b class="bf">write(<img src="images/img-0030.png" alt="$x$" style="vertical-align:0px;
width:10px;
height:8px" class="math gen" />)</b></big> <br />The write(<img src="images/img-0030.png" alt="$x$" style="vertical-align:0px;
width:10px;
height:8px" class="math gen" />) method writes the string <img src="images/img-0030.png" alt="$x$" style="vertical-align:0px;
width:10px;
height:8px" class="math gen" /> to a file. <a name="a0000000651" id="a0000000651"></a> </p></div>
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