Open the current base file with the (original) mode and encoding.
        Return the resulting stream.
        
        Note:  Copied from stdlib.  Added option to override 'mode'

def _open(self, mode=None):
        """
        Open the current base file with the (original) mode and encoding.
        Return the resulting stream.
        
        Note:  Copied from stdlib.  Added option to override 'mode'
        """
        if mode is None:
            mode = self.mode
        if self.encoding is None:
            stream = open(self.baseFilename, mode)
        else:
            stream = codecs.open(self.baseFilename, mode, self.encoding)
        return stream