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Mark Pilgrim
2009-07-18 00:43:19 -04:00
parent 7ba2d029fe
commit 9e03ab51aa
1 changed files with 48 additions and 20 deletions
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@@ -106,36 +106,35 @@ UnicodeDecodeError: 'charmap' codec can't decode byte 0x8f in position 28: chara
<pre class=screen>
# continued from the previous example
<a><samp class=p>>>> </samp><kbd class=pp>a_file.read()</kbd> <span class=u>&#x2460;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.read()</kbd> <span class=u>&#x2460;</span></a>
<samp class=pp>''</samp>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.seek(0)</kbd> <span class=u>&#x2461;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.seek(0)</kbd> <span class=u>&#x2461;</span></a>
<samp class=pp>0</samp>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.read(16)</kbd> <span class=u>&#x2462;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.read(16)</kbd> <span class=u>&#x2462;</span></a>
<samp class=pp>'Dive Into Python'</samp>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.read(1)</kbd> <span class=u>&#x2463;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.read(1)</kbd> <span class=u>&#x2463;</span></a>
<samp class=pp>' '</samp>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.read(1)</kbd> <span class=u>&#x2464;</span></a>
<samp class=p>>>> </samp><kbd class=pp>a_file.read(1)</kbd>
<samp class=pp>'是'</samp>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.tell()</kbd> <span class=u>&#x2465;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.tell()</kbd> <span class=u>&#x2464;</span></a>
<samp class=pp>20</samp></pre>
<ol>
<li>FIXME
<li>
<li>
<li>
<li>
<li>
<li>Since you&#8217;re still at the end of the file, further calls to the file object&#8217;s <code>read()</code> method simply return an empty string.
<li>The <code>seek()</code> method moves to a specific byte position in a file.
<li>The <code>read()</code> method can take an optional parameter, the number of characters to read.
<li>If you like, you can even read one character at a time.
<li>16 + 1 + 1 = &hellip; 20?
</ol>
<p>FIXME
<pre class=screen>
# continued from the previous example
<a><samp class=p>>>> </samp><kbd class=pp>a_file.seek(17)</kbd> <span class=u>&#x2460;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.seek(17)</kbd> <span class=u>&#x2460;</span></a>
<samp class=pp>17</samp>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.read(1)</kbd> <span class=u>&#x2461;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.read(1)</kbd> <span class=u>&#x2461;</span></a>
<samp class=pp>'是'</samp>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.tell()</kbd> <span class=u>&#x2462;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>a_file.tell()</kbd> <span class=u>&#x2462;</span></a>
<samp class=pp>20</samp></pre>
<ol>
<li>FIXME
@@ -206,13 +205,42 @@ ValueError: I/O operation on closed file.</samp>
<h3 id=for>Reading Data One Line At A Time</h3>
<p>A &#8220;line&#8221; of a text file is just what you think it is&nbsp;&mdash;&nbsp;you type a few words and press <kbd>ENTER</kbd>, and now you&#8217;re on a new line. A line of text is a sequence of characters delimited by&hellip; what exactly? Well, it&#8217;s complicated, because text files can use several different characters to mark the end of a line. Every operating system has its own convention. Some use a carriage return character, others use a line feed character, and some use both characters at the end of every line.
<p>Now breathe a sigh of relief, because <em>Python handles line endings automatically</em> by default. If you say, &#8220;I want to read this text file one line at a time,&#8221; Python will figure out which kind of line ending the text file uses and and it will all Just Work.
<blockquote class=note>
<p><span class=u>&#x261E;</span>If you need fine-grained control over what&#8217;s considered a line ending, you can pass the optional <code>newline</code> parameter to the <code>open()</code> function. See <a href=http://docs.python.org/3.1/library/io.html#module-interface>the <code>open()</code> function documentation</a> for all the gory details.
</blockquote>
<p>So, how do you actually do it? Read a file one line at a time, that is. It&#8217;s so simple, it&#8217;s beautiful.
<p class=d>[<a href=examples/oneline.py>download <code>oneline.py</code></a>]
<pre><code class=pp>line_number = 0
<a>with open('examples/favorite-people.txt', encoding='utf-8') as a_file: <span class=u>&#x2460;</span></a>
<a> for a_line in a_file: <span class=u>&#x2461;</span></a>
line_number += 1
<a> print('{} {}'.format(line_number, a_line.rstrip())) <span class=u>&#x2462;</span></a></code></pre>
<ol>
<li>FIXME
<li>
<li>
</ol>
<p>FIXME
<p>FIXME what's a "line"? (line endings discussion, universal line endings, etc.)
<!--
A &#8220;line&#8221; of a text file is just what you think it is&nbsp;&mdash;&nbsp;a sequence of characters delimited by a carriage return. Of course, it can&#8217;t really be that simple, can it? Text files can use several different characters to mark the end of a line. Some use a carriage return character, others use a line feed character, and some use both characters at the end of every line. Python handles all of these cases automatically, so you can say, &#8220;Hey, I want to read this text file one line at a time&#8221; and it will Just Work.
-->
<pre class=screen>
<samp class=p>you@localhost:~/diveintopython3$ </samp><kbd class=pp>python3 examples/oneline.py</kbd>
<samp class=pp>1 Dora
2 Ethan
3 Wesley
4 John
5 Anne
6 Mike
7 Chris
8 Sarah
9 Alex
10 Lizzie</samp></pre>
<h2 id=writing>Writing to Text Files</h2>