1 files changed, 66 insertions, 0 deletions
diff --git a/morphlib/savefile.py b/morphlib/savefile.py
new file mode 100644
index 00000000..902a9923
--- /dev/null
+++ b/morphlib/savefile.py
@@ -0,0 +1,66 @@
+# Copyright (C) 2012  Codethink Limited
+# 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; version 2 of the License.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+
+import os
+import tempfile
+
+class SaveFile(file):
+
+    '''Save files with a temporary name and rename when they're ready.
+    
+    This class acts exactly like the normal ``file`` class, except that
+    it is meant only for saving data to files. The data is written to
+    a temporary file, which gets renamed to the target name when the
+    open file is closed. This avoids readers of the file from getting
+    an incomplete file.
+    
+    Example:
+    
+        f = SaveFile('foo', 'w')
+        f.write(stuff)
+        f.close()
+        
+    The file will be called something like ``tmpCAFEBEEF`` until ``close``
+    is called, at which point it gets renamed to ``foo``.
+    
+    If the writer decides the file is not worth saving, they can call the
+    ``abort`` method, which deletes the temporary file.
+    
+    '''
+
+    def __init__(self, filename, *args, **kwargs):
+        self._savefile_filename = filename
+        dirname = os.path.dirname(filename)
+        fd, self._savefile_tempname = tempfile.mkstemp(dir=dirname)
+        os.close(fd)
+        file.__init__(self, self._savefile_tempname, *args, **kwargs)
+
+    def abort(self):
+        '''Abort file saving.
+        
+        The temporary file will be removed, and the universe is almost
+        exactly as if the file save had never started.
+        
+        '''
+
+        os.remove(self._savefile_tempname)
+        return file.close(self)
+
+    def close(self):
+        ret = file.close(self)
+        os.rename(self._savefile_tempname, self._savefile_filename)
+        return ret
+