def last_modified(self) -> str:
if self.name == "<STR_LIT>":<EOL><INDENT>if "<STR_LIT>" in self.ds._file["<STR_LIT>"].attrs:<EOL><INDENT>return self.ds._file["<STR_LIT>"].attrs["<STR_LIT>"]<EOL><DEDENT>elif self.ds._file.mode == '<STR_LIT>':<EOL><INDENT>self.ds._file["<STR_LIT>"].attrs["<STR_LIT>"] = timestamp()<EOL>self.ds._file.flush()<EOL>return self.ds._file["<STR_LIT>"].attrs["<STR_LIT>"]<EOL><DEDENT><DEDENT>if self.name != "<STR_LIT>":<EOL><INDENT>if "<STR_LIT>" in self.ds._file["<STR_LIT>" + self.name].attrs:<EOL><INDENT>return self.ds._file["<STR_LIT>" + self.name].attrs["<STR_LIT>"]<EOL><DEDENT>elif self.ds._file.mode == '<STR_LIT>':<EOL><INDENT>self.ds._file["<STR_LIT>" + self.name].attrs["<STR_LIT>"] = timestamp()<EOL>self.ds._file.flush()<EOL>return self.ds._file["<STR_LIT>" + self.name].attrs["<STR_LIT>"]<EOL><DEDENT><DEDENT>return timestamp()<EOL>
Return a compact ISO8601 timestamp (UTC timezone) indicating when the file was last modified

Note: if the layer does not contain a timestamp, and the mode is 'r+', a new timestamp will be set and returned.
Otherwise, the current time in UTC will be returned.