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<h2 class="title"><a name="fileinfo.summary2"></a>6.7. Summary
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<div class="abstract">
<p>The <tt class="filename">fileinfo.py</tt> program introduced in <a href="../object_oriented_framework/index.html">Chapter 5</a> should now make perfect sense.
</p>
</div>
<div class="informalexample"><pre class="programlisting">
<span class='pystring'>"""Framework for getting filetype-specific metadata.
Instantiate appropriate class with filename. Returned object acts like a
dictionary, with key-value pairs for each piece of metadata.
import fileinfo
info = fileinfo.MP3FileInfo("/music/ap/mahadeva.mp3")
print "\\n".join(["%s=%s" % (k, v) for k, v in info.items()])
Or use listDirectory function to get info on all files in a directory.
for info in fileinfo.listDirectory("/music/ap/", [".mp3"]):
...
Framework can be extended by adding classes for particular file types, e.g.
HTMLFileInfo, MPGFileInfo, DOCFileInfo. Each class is completely responsible for
parsing its files appropriately; see MP3FileInfo for example.
"""</span>
<span class='pykeyword'>import</span> os
<span class='pykeyword'>import</span> sys
<span class='pykeyword'>from</span> UserDict <span class='pykeyword'>import</span> UserDict
<span class='pykeyword'>def</span><span class='pyclass'> stripnulls</span>(data):
<span class='pystring'>"strip whitespace and nulls"</span>
<span class='pykeyword'>return</span> data.replace(<span class='pystring'>"\00"</span>, <span class='pystring'>""</span>).strip()
<span class='pykeyword'>class</span><span class='pyclass'> FileInfo</span>(UserDict):
<span class='pystring'>"store file metadata"</span>
<span class='pykeyword'>def</span><span class='pyclass'> __init__</span>(self, filename=None):
UserDict.__init__(self)
self[<span class='pystring'>"name"</span>] = filename
<span class='pykeyword'>class</span><span class='pyclass'> MP3FileInfo</span>(FileInfo):
<span class='pystring'>"store ID3v1.0 MP3 tags"</span>
tagDataMap = {<span class='pystring'>"title"</span> : ( 3, 33, stripnulls),
<span class='pystring'>"artist"</span> : ( 33, 63, stripnulls),
<span class='pystring'>"album"</span> : ( 63, 93, stripnulls),
<span class='pystring'>"year"</span> : ( 93, 97, stripnulls),
<span class='pystring'>"comment"</span> : ( 97, 126, stripnulls),
<span class='pystring'>"genre"</span> : (127, 128, ord)}
<span class='pykeyword'>def</span><span class='pyclass'> __parse</span>(self, filename):
<span class='pystring'>"parse ID3v1.0 tags from MP3 file"</span>
self.clear()
<span class='pykeyword'>try</span>:
fsock = open(filename, <span class='pystring'>"rb"</span>, 0)
<span class='pykeyword'>try</span>:
fsock.seek(-128, 2)
tagdata = fsock.read(128)
<span class='pykeyword'>finally</span>:
fsock.close()
<span class='pykeyword'>if</span> tagdata[:3] == <span class='pystring'>"TAG"</span>:
<span class='pykeyword'>for</span> tag, (start, end, parseFunc) <span class='pykeyword'>in</span> self.tagDataMap.items():
self[tag] = parseFunc(tagdata[start:end])
<span class='pykeyword'>except</span> IOError:
<span class='pykeyword'>pass</span>
<span class='pykeyword'>def</span><span class='pyclass'> __setitem__</span>(self, key, item):
<span class='pykeyword'>if</span> key == <span class='pystring'>"name"</span> <span class='pykeyword'>and</span> item:
self.__parse(item)
FileInfo.__setitem__(self, key, item)
<span class='pykeyword'>def</span><span class='pyclass'> listDirectory</span>(directory, fileExtList):
<span class='pystring'>"get list of file info objects for files of particular extensions"</span>
fileList = [os.path.normcase(f)
<span class='pykeyword'>for</span> f <span class='pykeyword'>in</span> os.listdir(directory)]
fileList = [os.path.join(directory, f)
<span class='pykeyword'>for</span> f <span class='pykeyword'>in</span> fileList
<span class='pykeyword'>if</span> os.path.splitext(f)[1] <span class='pykeyword'>in</span> fileExtList]
<span class='pykeyword'>def</span><span class='pyclass'> getFileInfoClass</span>(filename, module=sys.modules[FileInfo.__module__]):
<span class='pystring'>"get file info class from filename extension"</span>
subclass = <span class='pystring'>"%sFileInfo"</span> % os.path.splitext(filename)[1].upper()[1:]
<span class='pykeyword'>return</span> hasattr(module, subclass) <span class='pykeyword'>and</span> getattr(module, subclass) <span class='pykeyword'>or</span> FileInfo
<span class='pykeyword'>return</span> [getFileInfoClass(f)(f) <span class='pykeyword'>for</span> f <span class='pykeyword'>in</span> fileList]
<span class='pykeyword'>if</span> __name__ == <span class='pystring'>"__main__"</span>:
<span class='pykeyword'>for</span> info <span class='pykeyword'>in</span> listDirectory(<span class='pystring'>"/music/_singles/"</span>, [<span class='pystring'>".mp3"</span>]):
<span class='pykeyword'>print</span> <span class='pystring'>"\n"</span>.join([<span class='pystring'>"%s=%s"</span> % (k, v) <span class='pykeyword'>for</span> k, v <span class='pykeyword'>in</span> info.items()])
print</pre></div>
<div class="highlights">
<p>Before diving into the next chapter, make sure you're comfortable doing the following things:</p>
<div class="itemizedlist">
<ul>
<li>Catching exceptions with <a href="index.html#fileinfo.exception" title="6.1. Handling Exceptions"><tt class="literal">try...except</tt></a></li>
<li>Protecting external resources with <a href="file_objects.html#fileinfo.files.incode" title="Example 6.6. File Objects in MP3FileInfo"><tt class="literal">try...finally</tt></a></li>
<li>Reading from <a href="file_objects.html" title="6.2. Working with File Objects">files</a></li>
<li>Assigning multiple values at once in a <a href="for_loops.html#fileinfo.multiassign.for.example" title="Example 6.11. for Loop in MP3FileInfo"><tt class="literal">for</tt> loop</a></li>
<li>Using the <a href="os_module.html" title="6.5. Working with Directories"><tt class="filename">os</tt></a> module for all your cross-platform file manipulation needs
</li>
<li>Dynamically <a href="all_together.html" title="6.6. Putting It All Together">instantiating classes of unknown type</a> by treating classes as objects and passing them around
</li>
</ul>
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<td width="35%" align="left"><br><a class="NavigationArrow" href="all_together.html"><< Putting It All Together</a></td>
<td width="30%" align="center"><br> <span class="divider">|</span> <a href="index.html#fileinfo.exception" title="6.1. Handling Exceptions">1</a> <span class="divider">|</span> <a href="file_objects.html" title="6.2. Working with File Objects">2</a> <span class="divider">|</span> <a href="for_loops.html" title="6.3. Iterating with for Loops">3</a> <span class="divider">|</span> <a href="more_on_modules.html" title="6.4. Using sys.modules">4</a> <span class="divider">|</span> <a href="os_module.html" title="6.5. Working with Directories">5</a> <span class="divider">|</span> <a href="all_together.html" title="6.6. Putting It All Together">6</a> <span class="divider">|</span> <span class="thispage">7</span> <span class="divider">|</span>
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