code: def readline(self):
          
          if self.line_number >= self.total_lines:
              return ''
          line = self.lines[self.line_number]
          self.line_number += 1
          if self.indent_char is None and line[:1] in WHITESPACE:
              self.indent_char = line[0]
          return line
docs: Get the next line from the input buffer.