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<div class="section" id="using-hooks">
<h1>Using hooks<a class="headerlink" href="#using-hooks" title="Permalink to this headline">¶</a></h1>
<div class="section" id="what-is-a-hook">
<h2>What is a hook?<a class="headerlink" href="#what-is-a-hook" title="Permalink to this headline">¶</a></h2>
<p>One way to customize Bazaar’s behaviour is with <em>hooks</em>. Hooks allow you to
perform actions before or after certain Bazaar operations. The operations
include <tt class="docutils literal"><span class="pre">commit</span></tt>, <tt class="docutils literal"><span class="pre">push</span></tt>, <tt class="docutils literal"><span class="pre">pull</span></tt>, and <tt class="docutils literal"><span class="pre">uncommit</span></tt>.
For a complete list of hooks and their parameters, see <a class="reference external" href="../user-reference/index.html#hooks">Hooks</a> in the User Reference.</p>
<p>Most hooks are run on the client, but a few are run on the server. (Also
see the <a class="reference external" href="http://doc.bazaar.canonical.com/plugins/en/push-and-update-plugin.html">push-and-update plugin</a> that handles one special case of
server-side operations.)</p>
</div>
<div class="section" id="id1">
<h2>Using hooks<a class="headerlink" href="#id1" title="Permalink to this headline">¶</a></h2>
<p>To use a hook, you should <a class="reference external" href="http://doc.bazaar.canonical.com/plugins/en/plugin-development.html">write a plugin</a>. Instead of
creating a new command, this plugin will define and install the hook. Here’s
an example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">bzrlib</span> <span class="kn">import</span> <span class="n">branch</span>
<span class="k">def</span> <span class="nf">post_push_hook</span><span class="p">(</span><span class="n">push_result</span><span class="p">):</span>
<span class="k">print</span> <span class="s">"The new revno is </span><span class="si">%d</span><span class="s">"</span> <span class="o">%</span> <span class="n">push_result</span><span class="o">.</span><span class="n">new_revno</span>
<span class="n">branch</span><span class="o">.</span><span class="n">Branch</span><span class="o">.</span><span class="n">hooks</span><span class="o">.</span><span class="n">install_named_hook</span><span class="p">(</span><span class="s">'post_push'</span><span class="p">,</span> <span class="n">post_push_hook</span><span class="p">,</span>
<span class="s">'My post_push hook'</span><span class="p">)</span>
</pre></div>
</div>
<p>To use this example, create a file named <tt class="docutils literal"><span class="pre">push_hook.py</span></tt>, and stick it in
<tt class="docutils literal"><span class="pre">plugins</span></tt> subdirectory of your configuration directory. (If you have never
installed any plugins, you may need to create the <tt class="docutils literal"><span class="pre">plugins</span></tt> directory).</p>
<p>That’s it! The next time you push, it should show “The new revno is...”.
Of course, hooks can be much more elaborate than this, because you have the
full power of Python at your disposal. Now that you know how to use hooks,
what you do with them is up to you.</p>
<p>The plugin code does two things. First, it defines a function that will be
run after <tt class="docutils literal"><span class="pre">push</span></tt> completes. (It could instead use an instance method or
a callable object.) All push hooks take a single argument, the
<tt class="docutils literal"><span class="pre">push_result</span></tt>.</p>
<p>Second, the plugin installs the hook. The first argument <tt class="docutils literal"><span class="pre">'post_push'</span></tt>
identifies where to install the hook. The second argument is the hook
itself. The third argument is a name <tt class="docutils literal"><span class="pre">'My</span> <span class="pre">post_push</span> <span class="pre">hook'</span></tt>, which can be
used in progress messages and error messages.</p>
<p>To reduce the start-up time of Bazaar it is also possible to “lazily” install hooks,
using the <tt class="docutils literal"><span class="pre">bzrlib.hooks.install_lazy_named_hook</span></tt> function. This removes the need
to load the module that contains the hook point just to install the hook. Here’s lazy
version of the example above:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">bzrlib</span> <span class="kn">import</span> <span class="n">hooks</span>
<span class="k">def</span> <span class="nf">post_push_hook</span><span class="p">(</span><span class="n">push_result</span><span class="p">):</span>
<span class="k">print</span> <span class="s">"The new revno is </span><span class="si">%d</span><span class="s">"</span> <span class="o">%</span> <span class="n">push_result</span><span class="o">.</span><span class="n">new_revno</span>
<span class="n">hooks</span><span class="o">.</span><span class="n">install_lazy_named_hook</span><span class="p">(</span><span class="s">'bzrlib.branch'</span><span class="p">,</span> <span class="s">'Branch.hooks'</span><span class="p">,</span>
<span class="s">'post_push'</span><span class="p">,</span> <span class="n">post_push_hook</span><span class="p">,</span> <span class="s">'My post_push hook'</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="debugging-hooks">
<h2>Debugging hooks<a class="headerlink" href="#debugging-hooks" title="Permalink to this headline">¶</a></h2>
<p>To get a list of installed hooks (and available hook points), use the hidden
<tt class="docutils literal"><span class="pre">hooks</span></tt> command:</p>
<div class="highlight-python"><div class="highlight"><pre>bzr hooks
</pre></div>
</div>
</div>
<div class="section" id="example-a-merge-plugin">
<h2>Example: a merge plugin<a class="headerlink" href="#example-a-merge-plugin" title="Permalink to this headline">¶</a></h2>
<p>Here’s a complete plugin that demonstrates the <tt class="docutils literal"><span class="pre">Merger.merge_file_content</span></tt>
hook. It installs a hook that forces any merge of a file named <tt class="docutils literal"><span class="pre">*.xml</span></tt>
to be a conflict, even if Bazaar thinks it can merge it cleanly.</p>
<p><tt class="docutils literal"><span class="pre">merge_xml.py</span></tt>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="sd">"""Custom 'merge' logic for *.xml files.</span>
<span class="sd">Always conflicts if both branches have changed the file.</span>
<span class="sd">"""</span>
<span class="kn">from</span> <span class="nn">bzrlib.merge</span> <span class="kn">import</span> <span class="n">PerFileMerger</span><span class="p">,</span> <span class="n">Merger</span>
<span class="k">def</span> <span class="nf">merge_xml_files_hook</span><span class="p">(</span><span class="n">merger</span><span class="p">):</span>
<span class="sd">"""Hook to merge *.xml files"""</span>
<span class="k">return</span> <span class="n">AlwaysConflictXMLMerger</span><span class="p">(</span><span class="n">merger</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">AlwaysConflictXMLMerger</span><span class="p">(</span><span class="n">PerFileMerger</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">file_matches</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">params</span><span class="p">):</span>
<span class="n">filename</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">get_filename</span><span class="p">(</span><span class="n">params</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">merger</span><span class="o">.</span><span class="n">this_tree</span><span class="p">)</span>
<span class="k">return</span> <span class="n">filename</span><span class="o">.</span><span class="n">endswith</span><span class="p">(</span><span class="s">'.xml'</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">merge_matching</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">params</span><span class="p">):</span>
<span class="k">return</span> <span class="s">'conflicted'</span><span class="p">,</span> <span class="n">params</span><span class="o">.</span><span class="n">this_lines</span>
<span class="n">Merger</span><span class="o">.</span><span class="n">hooks</span><span class="o">.</span><span class="n">install_named_hook</span><span class="p">(</span>
<span class="s">'merge_file_content'</span><span class="p">,</span> <span class="n">merge_xml_files_hook</span><span class="p">,</span> <span class="s">'*.xml file merge'</span><span class="p">)</span>
</pre></div>
</div>
<p><tt class="docutils literal"><span class="pre">merge_file_content</span></tt> hooks are executed for each file to be merged. For
a more a complex example look at the <tt class="docutils literal"><span class="pre">news_merge</span></tt> plugin that’s bundled with
Bazaar in the <tt class="docutils literal"><span class="pre">bzrlib/plugins</span></tt> directory.</p>
</div>
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<h3><a href="../index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Using hooks</a><ul>
<li><a class="reference internal" href="#what-is-a-hook">What is a hook?</a></li>
<li><a class="reference internal" href="#id1">Using hooks</a></li>
<li><a class="reference internal" href="#debugging-hooks">Debugging hooks</a></li>
<li><a class="reference internal" href="#example-a-merge-plugin">Example: a merge plugin</a></li>
</ul>
</li>
</ul>
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