def log_dir(self) -> str:
        """The directory for this run's tensorboard checkpoint.

        By default, it is named ``'version_${self.version}'`` but it can be overridden by passing a string value for the
        constructor's version parameter instead of ``None`` or an int.

        """
        version = self.version if isinstance(self.version, str) else f"version_{self.version}"
        log_dir = os.path.join(self.root_dir, self.name, version)
        if isinstance(self.sub_dir, str):
            log_dir = os.path.join(log_dir, self.sub_dir)
        log_dir = os.path.expandvars(log_dir)
        log_dir = os.path.expanduser(log_dir)
        return log_dir
The directory for this run's tensorboard checkpoint.

        By default, it is named ``'version_${self.version}'`` but it can be overridden by passing a string value for the
        constructor's version parameter instead of ``None`` or an int.

        
src/lightning/fabric/loggers/tensorboard.py