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annotate docs/api/01_plugins.md @ 550:6f216c1ab6b1

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author Ludovic Chabant <ludovic@chabant.com>
date Tue, 04 Aug 2015 21:22:30 -0700
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1 ---
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2 title: Plugins
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3 ---
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4
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5 To create a PieCrust plugin, you need to do a few things:
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7 * Create a correct `setuptools` package.
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8 * Implement a sub-class of `PieCrustPlugin`.
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9 * Write a couple lines of boilerplate code.
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12 ## Packaging plugins
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14 PieCrust plugins are expected to be available on [Pypi][] for better integration
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15 with `chef` commands. For instance, the `chef plugins list -a` will list all
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16 PieCrust plugins from Pypi.
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17
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18 A PieCrust plugin package must:
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19
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20 * Be named `PieCrust-FooBar`, where `FooBar` is the name of the plugin.
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21 * Have a module named `piecrust_foobar`, which is basically the lower-case
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22 version of the package name, with an underscore instead of a dash.
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24 You can refer to the [`setuptools` documentation][st] for more information.
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27 ## The plugin class
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28
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29 A PieCrust plugin is an instance of a class that derives from `PieCrustPlugin`.
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30 The only required thing you need to override is the name of the plugin:
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31
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32 from piecrust.plugins.base import PieCrustPlugin
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33
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34 class FooBarPlugin(PieCrustPlugin):
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35 name = 'FooBar'
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36
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37 The plugin class has a whole bunch of functions returning whatever your plugin
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38 may want to extend: formatters, template engines, `chef` commands, sources, etc.
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39 Each one of those returns an array of instances or classes, depending on the
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40 situation.
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41
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42 Check the `piecrust.plugins.builtin.BuiltInPlugin` to see how all PieCrust
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43 functionality is implemented.
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45
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46 ## Boilerplate code
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47
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48 Now we have a plugin class, and a Pypi package that PieCrust can find if needed.
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49 All we need is a way to tell PieCrust how to find your plugin class in that
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50 package.
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51
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52 In the required `piecrust_foobar` module, you need to define a
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53 `__piecrust_plugin__` global variable that points to your plugin class:
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55 __piecrust_plugin__ = FooBarPlugin
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56
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57 That's what PieCrust will use to instantiate your plugin.
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60 ## Loading the plugin
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61
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62 Now you can add your plugin to a PieCrust website by adding this to the website
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63 configuration:
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64
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65 site:
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66 plugins: foobar
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67
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68 PieCrust will prepend `piecrust_` to each specified plugin name and attempt to
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69 load that as a module (`import piecrust_foobar`). If this succeeds, it will look
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70 for a `__piecrust_plugin__` in that module, and expect its value to be a class
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71 that inherits from `PieCrustPlugin`. If everything's OK, it will instantiate
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72 that class and query it for various services and components when necessary.
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73
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74
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75 [pypi]: https://pypi.python.org/pypi
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76 [st]: http://pythonhosted.org/setuptools/
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