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split final dictionary comprehension example into two steps to make the progression more clear and to avoid calling os.stat twice on each file

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Mark Pilgrim
2009-09-17 18:08:20 -04:00
parent 9c21653c7d
commit 3937e1f06b
1 changed files with 7 additions and 5 deletions
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comprehensions.html
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@@ -293,14 +293,16 @@ body{counter-reset:h1 3}
<pre class=screen>
<samp class=p>>>> </samp><kbd class=pp>import os, glob, humansize</kbd>
<a><samp class=p>>>> </samp><kbd class=pp>humansize_dict = {os.path.splitext(f)[0]:humansize.approximate_size(os.stat(f).st_size) \ </kbd>
<samp class=p>... </samp><kbd class=pp> for f in glob.glob('*') if os.stat(f).st_size > 6000}</kbd> <span class=u>&#x2460;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>list(humansize_dict.keys())</kbd> <span class=u>&#x2461;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>metadata_dict = {f:os.stat(f) for f in glob.glob('*')}</kbd> <span class=u>&#x2460;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>humansize_dict = {os.path.splitext(f)[0]:humansize.approximate_size(meta.st_size) \ </kbd>
<samp class=p>... </samp><kbd class=pp> for f, meta in metadata_dict.items() if meta.st_size > 6000}</kbd> <span class=u>&#x2461;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>list(humansize_dict.keys())</kbd> <span class=u>&#x2462;</span></a>
<samp class=pp>['romantest9', 'romantest8', 'romantest7', 'romantest6', 'romantest10', 'pluraltest6']</samp>
<a><samp class=p>>>> </samp><kbd class=pp>humansize_dict['romantest9']</kbd> <span class=u>&#x2462;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>humansize_dict['romantest9']</kbd> <span class=u>&#x2463;</span></a>
<samp class=pp>'6.5 KiB'</samp></pre>
<ol>
<li>This dictionary comprehension constructs a list of all the files in the current working directory (<code>glob.glob('*')</code>), filters that list to include only those files larger than <code>6000</code> bytes (<code>if os.stat(f).st_size > 6000</code>), and uses that filtered list to construct a dictionary whose keys are the filename minus the extension (<code>os.path.splitext(f)[0]</code>) and whose values are the approximate size of each file (<code>humansize.approximate_size(os.stat(f).st_size)</code>).
<li>This dictionary comprehension constructs a list of all the files in the current working directory (<code>glob.glob('*')</code>), gets the file metadata for each file (<code>os.stat(f)</code>), and constructs a dictionary whose keys are filenames and whose values are the metadata for each file.
<li>This dictionary comprehension builds on the previous comprehension, filters out files smaller than <code>6000</code> bytes (<code>if meta.st_size > 6000</code>), and uses that filtered list to construct a dictionary whose keys are the filename minus the extension (<code>os.path.splitext(f)[0]</code>) and whose values are the approximate size of each file (<code>humansize.approximate_size(meta.st_size)</code>).
<li>As you saw in a previous example, there are six such files, thus there are six items in this dictionary.
<li>The value of each key is the string returned from the <code>approximate_size()</code> function.
</ol>