* morituri/common/common.py:

Create a Persister class to wrap a possible pickle path.
	* examples/trm.py:
	  Use it.

morituri/common/common.py

@@ -20,6 +20,10 @@
 # You should have received a copy of the GNU General Public License
 # along with morituri.  If not, see <http://www.gnu.org/licenses/>.
 
+import os
+import tempfile
+import shutil
+
 def msfToFrames(msf):
     """
     Converts a string value in MM:SS:FF to frames
@@ -57,3 +61,71 @@ def framesToHMSF(frames):
     h = frames / 75 / 60 / 60
 
     return "%02d:%02d:%02d.%02d" % (h, m, s, f)
+
+class Persister(object):
+    """
+    I wrap an optional pickle to persist an object to disk.
+
+    Instantiate me with a path to automatically unpickle the object.
+    Call persist to store the object to disk; it will get stored if it
+    changed from the on-disk object.
+
+    @ivar object: the persistent object
+    """
+
+    def __init__(self, path=None, default=None):
+        """
+        If path is not given, the object will not be persisted.
+        This allows code to transparently deal with both persisted and
+        non-persisted objects, since the persist method will just end up
+        doing nothing.
+        """
+        self._path = path
+        self.object = None
+
+        self._unpickle(default)
+
+    def persist(self, object=None):
+        """
+        Persist the given object, if we have a persistence path and the
+        object changed.
+
+        If object is not given, re-persist our object, always.
+        If object is given, only persist if it was changed.
+        """
+        # don't pickle if it's already ok
+        if object and object == self.object:
+            return
+
+        # don't pickle if there is no path
+        if not self._path:
+            return
+
+        # default to pickling our object again
+        if object is None:
+            object = self.object
+
+        # pickle
+        self.object = object
+        (fd, path) = tempfile.mkstemp(suffix='.morituri.pickle')
+        handle = os.fdopen(fd, 'wb')
+        print 'pickle'
+        import pickle
+        pickle.dump(object, handle, 2)
+        handle.close()
+        # do an atomic move
+        shutil.move(path, self._path)
+
+    def _unpickle(self, default=None):
+        self.object = default
+
+        if not self._path:
+            return None
+
+        if not os.path.exists(self._path):
+            return None
+
+        handle = open(self._path)
+        import pickle
+        print 'unpickle'
+        self.object = pickle.load(handle)