def __call__(self,index=None):
index = self._get_index(index)<EOL>if index is None:<EOL><INDENT>return<EOL><DEDENT>try:<EOL><INDENT>marquee = self.marquee<EOL>next_block = self.src_blocks[index]<EOL>self.block_index += <NUM_LIT:1><EOL>if self._silent[index]:<EOL><INDENT>print(marquee('<STR_LIT>' %<EOL>(index,self.nblocks-index-<NUM_LIT:1>)), file=io.stdout)<EOL><DEDENT>else:<EOL><INDENT>self.pre_cmd()<EOL>self.show(index)<EOL>if self.auto_all or self._auto[index]:<EOL><INDENT>print(marquee('<STR_LIT>'), file=io.stdout)<EOL><DEDENT>else:<EOL><INDENT>print(marquee('<STR_LIT>'), end='<STR_LIT:U+0020>', file=io.stdout)<EOL>ans = input().strip()<EOL>if ans:<EOL><INDENT>print(marquee('<STR_LIT>'), file=io.stdout)<EOL>return<EOL><DEDENT><DEDENT><DEDENT>try:<EOL><INDENT>save_argv = sys.argv<EOL>sys.argv = self.sys_argv<EOL>self.run_cell(next_block)<EOL>self.post_cmd()<EOL><DEDENT>finally:<EOL><INDENT>sys.argv = save_argv<EOL><DEDENT><DEDENT>except:<EOL><INDENT>self.ip_showtb(filename=self.fname)<EOL><DEDENT>else:<EOL><INDENT>self.ip_ns.update(self.user_ns)<EOL><DEDENT>if self.block_index == self.nblocks:<EOL><INDENT>mq1 = self.marquee('<STR_LIT>')<EOL>if mq1:<EOL><INDENT>print(file=io.stdout)<EOL>print(mq1, file=io.stdout)<EOL>print(self.marquee('<STR_LIT>'), file=io.stdout)<EOL><DEDENT>self.finished = True<EOL><DEDENT>
run a block of the demo.

        If index is given, it should be an integer >=1 and <= nblocks.  This
        means that the calling convention is one off from typical Python
        lists.  The reason for the inconsistency is that the demo always
        prints 'Block n/N, and N is the total, so it would be very odd to use
        zero-indexing here.