code: def point(self, x, y, char):
          
          assert len(char) == 1
          assert x >= 0
          assert x < self.cols
          assert y >= 0
          assert y < self.lines
  
          self.canvas[y][x] = char
docs: Create a point on ASCII canvas.
  
          Args:
              x (int): x coordinate. Should be >= 0 and < number of columns in
                  the canvas.
              y (int): y coordinate. Should be >= 0 an < number of lines in the
                  canvas.
              char (str): character to place in the specified point on the
                  canvas.