ubuntutools.misc: Add a new "system_distribution_chain", which returns

a list starting with the current distribution and working its way up
each distribution's parent.

debian/changelog

@@ -22,7 +22,12 @@ ubuntu-dev-tools (0.125) UNRELEASED; urgency=low
   * lp-project-upload:
     - fix a bug when new milestone wasn't specified
 
- -- Benjamin Drung <bdrung@debian.org>  Sat, 28 May 2011 19:43:10 +0200
+  [ Evan Broder ]
+  * ubuntutools.misc: Add a new "system_distribution_chain", which returns
+    a list starting with the current distribution and working its way up
+    each distribution's parent.
+
+ -- Evan Broder <evan@ebroder.net>  Sat, 11 Jun 2011 05:05:21 -0700
 
 ubuntu-dev-tools (0.124) unstable; urgency=low
 

ubuntutools/misc.py

@@ -4,6 +4,7 @@
 # Copyright (C) 2008,      Jonathan Davies <jpds@ubuntu.com>,
 #               2008-2009, Siegfried-Angel Gevatter Pujals <rainct@ubuntu.com>,
 #               2010,      Stefano Rivera <stefanor@ubuntu.com>
+#               2011,      Evan Broder <evan@ebroder.net>
 #
 # ##################################################################
 #
@@ -30,7 +31,46 @@ import sys
 
 from ubuntutools.lp.udtexceptions import PocketDoesNotExistError
 
-_system_distribution = None
+_system_distribution_chain = []
+def system_distribution_chain():
+    """ system_distribution_chain() -> [string]
+
+    Detect the system's distribution as well as all of its parent
+    distributions and return them as a list of strings, with the
+    system distribution first (and the greatest grandparent last). If
+    the distribution chain can't be determined, print an error message
+    and return an empty list.
+    """
+    global _system_distribution_chain
+    if len(_system_distribution_chain) == 0:
+        try:
+            p = Popen(('dpkg-vendor', '--query', 'Vendor'),
+                      stdout=PIPE)
+            _system_distribution_chain.append(p.communicate()[0].strip())
+        except OSError:
+            print ('Error: Could not determine what distribution you are '
+                   'running.')
+            return []
+
+        while True:
+            try:
+                p = Popen(('dpkg-vendor',
+                           '--vendor', _system_distribution_chain[-1],
+                           '--query', 'Parent'),
+                          stdout=PIPE)
+                parent = p.communicate()[0].strip()
+                # Don't check return code, because if a vendor has no
+                # parent, dpkg-vendor returns 1
+                if not parent:
+                    break
+                _system_distribution_chain.append(parent)
+            except Exception:
+                print ('Error: Could not determine the parent of the '
+                       'distribution %s' % _system_distribution_chain[-1])
+                return []
+
+    return _system_distribution_chain
+
 def system_distribution():
     """ system_distro() -> string
 
@@ -38,24 +78,7 @@ def system_distribution():
     name of the distribution can't be determined, print an error message
     and return None.
     """
-    global _system_distribution
-    if _system_distribution is None:
-        try:
-            if os.path.isfile('/usr/bin/dpkg-vendor'):
-                process = Popen(('dpkg-vendor', '--query', 'vendor'),
-                                stdout=PIPE)
-            else:
-                process = Popen(('lsb_release', '-cs'), stdout=PIPE)
-            output = process.communicate()[0]
-        except OSError:
-            print ('Error: Could not determine what distribution you are '
-                   'running.')
-            return None
-        if process.returncode != 0:
-            print 'Error determininng system distribution'
-            return None
-        _system_distribution = output.strip()
-    return _system_distribution
+    return system_distribution_chain()[0]
 
 def host_architecture():
     """ host_architecture -> string