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Python/Closures - Revision history
2024-03-28T10:14:26Z
Revision history for this page on the wiki
MediaWiki 1.41.0
https://grasswiki.osgeo.org/w/index.php?title=Python/Closures&diff=19700&oldid=prev
Neteler: +category
2013-09-09T19:39:28Z
<p>+category</p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td>
<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 19:39, 9 September 2013</td>
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<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div> </div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">{{Python}}</ins></div></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>=Why are useful=</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>=Why <ins style="font-weight: bold; text-decoration: none;">Closures </ins>are useful=</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>A closure is a way to define a variable statically into a function. They are good to:</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>A closure is a way to define a variable statically into a function. They are good to:</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Replace hard coded constants;</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Replace hard coded constants;</div></td></tr>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><source lang="python"></div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><source lang="python"></div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>from grass.pygrass.modules import Module</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>from grass.pygrass.modules import Module</div></td></tr>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>def get_module(cmd):</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>def get_module(cmd):</div></td></tr>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Note: This example doesn't work with multiprocessing.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Note: This example doesn't work with multiprocessing.</div></td></tr>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
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Neteler
https://grasswiki.osgeo.org/w/index.php?title=Python/Closures&diff=19699&oldid=prev
⚠️Pietro: Add a new page
2013-09-09T19:32:52Z
<p>Add a new page</p>
<p><b>New page</b></p><div><br />
=Why are useful=<br />
A closure is a way to define a variable statically into a function. They are good to:<br />
* Replace hard coded constants;<br />
* Eliminate globals.<br />
<br />
=Some examples=<br />
<br />
Define a function that return another function:<br />
<br />
<source lang="python"><br />
def print_something(msg):<br />
def _print(var):<br />
print msg % var<br />
return _print<br />
</source><br />
<br />
Now we can use to instantiate the function and define the string formatting statically and then call the returned function.<br />
<br />
<source lang="python"><br />
>>> p = print_something('Hi %s!')<br />
>>> p('Pietro')<br />
Hi Pietro!<br />
</source><br />
<br />
Now a more interesting example for the grass users:<br />
<br />
<source lang="python"><br />
from grass.pygrass.modules import Module<br />
<br />
<br />
def get_module(cmd):<br />
mod = Module(cmd)<br />
<br />
def do(**kwargs):<br />
mod(**kwargs)<br />
return do<br />
</source><br />
<br />
If we test the speed of a GRASS module, using ipython I got:<br />
<br />
<source lang="python"><br />
>>> %timeit Module('g.region', flags='p')<br />
10 loops, best of 3: 30.8 ms per loop<br />
</source><br />
<br />
Instead, using the python closure, I got:<br />
<br />
<source lang="python"><br />
>>> greg = get_module('g.region')<br />
>>> %timeit greg(flags='p')<br />
100 loops, best of 3: 12.8 ms per loop<br />
</source><br />
<br />
Note: This example doesn't work with multiprocessing.<br />
<br />
<br />
=References=<br />
* [http://ynniv.com/blog/2007/08/closures-in-python.html Closures in Python]<br />
* [http://www.shutupandship.com/2012/01/python-closures-explained.html Python closures explained]<br />
* [http://effbot.org/zone/closure.htm Closure]</div>
⚠️Pietro