Discover plugins in system directories too

README.md

@@ -265,14 +265,31 @@ python2 -m whipper -h
 
 ## Logger plugins
 
-Whipper supports using external logger plugins to write rip `.log` files.
+Whipper allows using external logger plugins to customize the template of `.log` files.
 
-List available plugins with `whipper cd rip -h`. Specify a logger to rip with by passing `-L loggername`:
+The available plugins can be listed with `whipper cd rip -h`. Specify a logger to rip with by passing `-L loggername`:
 
 ```bash
-whipper cd rip -L what
+whipper cd rip -L eac
 ```
 
+Whipper searches for logger plugins in the following paths:
+
+- `$XDG_DATA_HOME/whipper/plugins`
+- Paths returned by the following Python instruction:
+
+  `[x + '/whipper/plugins' for x in site.getsitepackages()]`
+
+- If whipper is run in a `virtualenv`, it will use these alternative instructions (from `distutils.sysconfig`):
+  - `get_python_lib(plat_specific=False, standard_lib=False, prefix='/usr/local') + '/whipper/plugins'`
+  - `get_python_lib(plat_specific=False, standard_lib=False) + '/whipper/plugins'`
+
+On a default Debian/Ubuntu installation, the following paths are searched by whipper:
+
+- `$HOME/.local/share/whipper/plugins`
+- `/usr/local/lib/python2.7/dist-packages/whipper/plugins`
+- `/usr/lib/python2.7/dist-packages/whipper/plugins`
+
 ### Official logger plugins
 
 I suggest using whipper's default logger unless you've got particular requirements.

whipper/command/main.py

@@ -5,9 +5,9 @@
 import sys
 import pkg_resources
 import musicbrainzngs
-
+import site
 import whipper
-
+from distutils.sysconfig import get_python_lib
 from whipper.command import cd, offset, drive, image, accurip, mblookup
 from whipper.command.basecommand import BaseCommand
 from whipper.common import common, directory, config
@@ -21,9 +21,21 @@
 def main():
     server = config.Config().get_musicbrainz_server()
     musicbrainzngs.set_hostname(server)
+
+    # Find whipper's plugins paths (local paths have higher priority)
+    plugins_p = [directory.data_path('plugins')]  # local path (in $HOME)
+    if hasattr(sys, 'real_prefix'):  # no getsitepackages() in virtualenv
+        plugins_p.append(
+            get_python_lib(plat_specific=False, standard_lib=False,
+                           prefix='/usr/local') + '/whipper/plugins')
+        plugins_p.append(get_python_lib(plat_specific=False,
+                         standard_lib=False) + '/whipper/plugins')
+    else:
+        plugins_p += [x + '/whipper/plugins' for x in site.getsitepackages()]
+
     # register plugins with pkg_resources
     distributions, _ = pkg_resources.working_set.find_plugins(
-        pkg_resources.Environment([directory.data_path('plugins')])
+        pkg_resources.Environment(plugins_p)
     )
     list(map(pkg_resources.working_set.add, distributions))
     try: