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examples for #read

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Mark Pilgrim
2009-07-17 11:40:13 -04:00
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@@ -89,32 +89,60 @@ UnicodeDecodeError: 'charmap' codec can't decode byte 0x8f in position 28: chara
<h3 id=read>Reading Data From A Text File</h3>
<p>After you open a file for reading, you&#8217;ll probably want to read from it at some point.
<pre class=screen>
<samp class=p>>>> </samp><kbd class=pp>a_file = open('examples/chinese.txt', encoding='utf-8')</kbd>
<samp class=p>>>> </samp><kbd class=pp>a_file.read()</kbd>
<samp class=pp>'Dive Into Python 是为有经验的程序员编写的一本 Python 书。\n'</samp></pre>
<ol>
<li>FIXME
</ol>
<p>FIXME
<!--
<p>After you open a file, the first thing you&#8217;ll want to do is read from it, as shown in the next example.
<div class=example><h3>Example 6.4. Reading a File</h3><pre class=screen>
<samp class=p>>>> </samp><kbd>f</kbd>
&lt;open file '/music/_singles/kairo.mp3', mode 'rb' at 010E3988>
<samp class=p>>>> </samp><kbd>f.tell()</kbd> <span>&#x2460;</span>
0
<samp class=p>>>> </samp><kbd>f.seek(-128, 2)</kbd> <span>&#x2461;</span>
<samp class=p>>>> </samp><kbd>f.tell()</kbd> <span>&#x2462;</span>
7542909
<samp class=p>>>> </samp><kbd>tagData = f.read(128)</kbd> <span>&#x2463;</span>
<samp class=p>>>> </samp><kbd>tagData</kbd>
<samp>'TAGKAIRO****THE BEST GOA ***DJ MARY-JANE***
Rave Mix 2000http://mp3.com/DJMARYJANE \037'</samp>
<samp class=p>>>> </samp><kbd>f.tell()</kbd> <span>&#x2464;</span>
7543037</pre>
<pre class=screen>
<samp class=p>>>> </samp><kbd class=pp>a_file.seek(0)</kbd>
<samp class=pp>0</samp>
<samp class=p>>>> </samp><kbd class=pp>a_file.read(16)</kbd>
<samp class=pp>'Dive Into Python'</samp>
<samp class=p>>>> </samp><kbd class=pp>a_file.read(1)</kbd>
<samp class=pp>' '</samp>
<samp class=p>>>> </samp><kbd class=pp>a_file.read(1)</kbd>
<samp class=pp>'是'</samp>
<samp class=p>>>> </samp><kbd class=pp>a_file.tell()</kbd>
<samp class=pp>20</samp></pre>
<ol>
<li>A file object maintains state about the file it has open. The <code>tell</code> method of a file object tells you your current position in the open file. Since you haven&#8217;t done anything with this file yet, the current position is <code>0</code>, which is the beginning of the file.
<li>The <code>seek</code> method of a file object moves to another position in the open file. The second parameter specifies what the first one means;
<code>0</code> means move to an absolute position (counting from the start of the file), <code>1</code> means move to a relative position (counting from the current position), and <code>2</code> means move to a position relative to the end of the file. Since the <abbr>MP3</abbr> tags you&#8217;re looking for are stored at the end of the file, you use <code>2</code> and tell the file object to move to a position <code>128</code> bytes from the end of the file.
<li>The <code>tell</code> method confirms that the current file position has moved.
<li>The <code>read</code> method reads a specified number of bytes from the open file and returns a string with the data that was read. The optional parameter specifies the maximum number of bytes to read. If no parameter is specified, <code>read</code> will read until the end of the file. (You could have simply said <code>read()</code> here, since you know exactly where you are in the file and you are, in fact, reading the last 128 bytes.) The read data is assigned to the <var>tagData</var> variable, and the current position is updated based on how many bytes were read.
<li>The <code>tell</code> method confirms that the current position has moved. If you do the math, you&#8217;ll see that after reading 128 bytes, the position has been incremented by 128.
-->
<li>FIXME
</ol>
<p>FIXME
<pre class=screen>
<samp class=p>>>> </samp><kbd class=pp>a_file.seek(17)</kbd>
<samp class=pp>17</samp>
<samp class=p>>>> </samp><kbd class=pp>a_file.read(1)</kbd>
<samp class=pp>'是'</samp>
<samp class=p>>>> </samp><kbd class=pp>a_file.tell()</kbd>
<samp class=pp>20</samp></pre>
<ol>
<li>FIXME
</ol>
<p>FIXME
<pre class=screen>
<samp class=p>>>> </samp><kbd class=pp>a_file.seek(18)</kbd>
<samp class=p>>>> </samp><kbd class=pp>a_file.read(1)</kbd>
<samp class=pp>Traceback (most recent call last):
File "&lt;pyshell#12>", line 1, in &lt;module>
a_file.read(1)
File "C:\Python31\lib\codecs.py", line 300, in decode
(result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf8' codec can't decode byte 0x98 in position 0: unexpected code byte</samp></pre>
<ol>
<li>FIXME
</ol>
<h3>6.2.2. Closing Files</h3>