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POPython: Test if dictionary (dict) entry has been modified
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copied!<p>I have written a small wrapper for the <code>dict</code> built-in class that loads entries (values) of a dictionary from <code>cPickle</code>d files as soon as the respective key is first accessed. When the dictionary is destroyed all loaded entries are written back to disk.</p> <p>Now it would be convenient if I could check if any of the values has been changed and write out only those that in fact have been. <strong>My question therefore is: Does a dictionary know if a value has been changed? Or is there a clever way to transparently implement this?</strong></p> <p>For completeness I attach the code I use. It's called with the path where the files are stored (keys are used as filenames) and with a list of keys for which files exist.</p> <pre><code>import cPickle class DictDB(dict): def __init__(self, path, folders): self.picklepath = path # path to files on disk self.folders = folders # available folders self.loaded_folders = {} def has_key(self, key): return key in self.folders def get(self, key): if not key in self.loaded_folders.keys(): if not key in self.folders: raise KeyError("Folder "+key+" not available") # load from disk self.loaded_folders[key] = cPickle.load(file(self.picklepath + key + ".cpickle2")) return self.loaded_folders[key] def __getitem__(self, key): return self.get(key) def close(self): for folder in self.loaded_folders.keys(): # write back cPickle.dump(self.loaded_folders[folder], file(picklepath + folder + '.cpickle2', 'w'), 2) def __del__(self): self.close() </code></pre>

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