def _init_data(self, suffix: str | bool | None) -> None:
        """Create a data file if we don't have one yet."""
        if self._data is None:
            # Create the data file.  We do this at construction time so that the
            # data file will be written into the directory where the process
            # started rather than wherever the process eventually chdir'd to.
            ensure_dir_for_file(self.config.data_file)
            self._data = CoverageData(
                basename=self.config.data_file,
                suffix=suffix,
                warn=self._warn,
                debug=self._debug,
                no_disk=self._no_disk,
            )
Create a data file if we don't have one yet.
coverage/control.py