code: def getKeyName(username, date, blob_key):
      
  
      sep = FileMetadata.__SEP
      return str(username + sep + str(date) + sep + blob_key)
docs: Returns the internal key for a particular item in the database.
  
      Our items are stored with keys of the form 'user/date/blob_key' ('/' is
      not the real separator, but __SEP is).
  
      Args:
        username: The given user's e-mail address.
        date: A datetime object representing the date and time that an input
          file was uploaded to this app.
        blob_key: The blob key corresponding to the location of the input file
          in the Blobstore.
      Returns:
        The internal key for the item specified by (username, date, blob_key).