英文文档：
ascii(object)
As repr(), return a string containing a printable representation of an object, but escape the non-ASCII characters in the string returned by repr() using \x, \u or \U escapes. This generates a string similar to that returned by repr() in Python 2.
返回对象的可打印表字符串表现方式
说明：
1. 返回一个可打印的对象字符串方式表示，如果是非ascii字符就会输出\x，\u或\U等字符来表示。与python2版本里的repr()是等效的函数。
>>> ascii(1)
'1'
>>> ascii('&')
"'&'"
>>> ascii(9000000)
'9000000'
>>> ascii('中文') #非ascii字符
"'\\u4e2d\\u6587'"