save the default array as a CSV file

def save_csv(self, filename, write_header_separately=True):
        """
        save the default array as a CSV file
        """
        txt = ''
        #print("SAVING arr = ", self.arr)
        
        with open(filename, "w") as f:
            if write_header_separately:
                f.write(','.join([c for c in self.header]) + '\n')
            for row in self.arr:
                #print('save_csv: saving row = ', row)
                txt = ','.join([self.force_to_string(col) for col in row])
                #print(txt)
                f.write(txt + '\n')
            f.write('\n')