def strip_unprintable_characters(self):
        """ Remove all non-printable characters from canvas """
        #frame_num = 0
        for frame in self.frames:
            line_num = 0
            col_num = 0
            for line in frame.content:
                for char in line:
                    if char.isprintable():
                        pass
                    else:   # Not a printable character, so replace it with a ' '
                        #line_str = line_str.replace(search_str, replace_str.ljust(len(search_str)))
                        #line = list(line_str)
                        frame.content[line_num][col_num] = ' '
                    col_num += 1
                col_num = 0
                line_num += 1
        return True
 Remove all non-printable characters from canvas 
durdraw/durdraw_movie.py