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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _FindFileContainingSymbolInDb(self, symbol):
 """Finds the file in descriptor DB containing the specified symbol. Args: symbol: The name of the symbol to search for. Returns: A FileDescriptor that contains the specified symbol. Raises: KeyError: if the file cannot be found in the descriptor database. """

    try:
      file_proto = self._internal_db.FindFileContainingSymbol(symbol)
    except KeyError as error:
      if self._descriptor_db:
        file_proto = self._descriptor_db.FindFileContainingSymbol(symbol)
      else:
        raise error
    if not file_proto:
      raise KeyError('Cannot find a file containing %s' % symbol)
    return self._ConvertFileProtoToFileDescriptor(file_proto)