class NoSuchStudentException(Exception):
    """Žiak nie je v zozname."""

class Garden():
    def __init__(self, diagram: str):
    self.diagram: str = diagram
    self.rows: str = diagram.splitlines()

    def add_rows(self,row):
        if isinstance(row,str):
            raise ValueError("Row has to be string")
        self.rows.append(row)

garden = Garden("VVCG\nWRC")
print([item[1:3] for item in garden.rows])
garden.rows.append(Garden("s\ns"))
print(garden.rows)