Return file name (ie. path) with the prefix directory prepended

def _prepend_name_prefix(self, name):
        """Return file name (ie. path) with the prefix directory prepended"""
        if not self.name_prefix:
            return name
        base = self.name_prefix
        if base[0] != '/':
            base = '/' + base
        if name[0] != '/':
            name = '/' + name
        return base + name