def rename_function(self, src_func, tgt_func):
        """
        Renames the function with function name (src_func) to (tgt_func)
        """
        if src_func not in self.functions:
            logger.warning("Couldn't find function name (%s).", src_func)
            return
        if tgt_func in self.functions:
            logger.warning("(%s) already exists in some function name.", tgt_func)
            return

        self.functions[tgt_func] = self.functions.pop(src_func)
        logger.debug(
            "Successfully changed function name from (%s) to (%s)", src_func, tgt_func
        )

        Renames the function with function name (src_func) to (tgt_func)
        
coremltools/converters/mil/frontend/tensorflow/tfssa.py