普通字符串可以用多种方式编码成Unicode字符串，具体要看你究竟选择了哪种编码：

unicodestring = u"Hello world"

# 将Unicode转化为普通Python字符串："encode" 

utf8string = unicodestring.encode("utf-8") 

asciistring = unicodestring.encode("ascii") 

isostring = unicodestring.encode("ISO-8859-1") 

utf16string = unicodestring.encode("utf-16") 

# 将普通Python字符串转化为Unicode："decode" 

plainstring1 = unicode(utf8string, "utf-8") 

plainstring2 = unicode(asciistring, "ascii") 

plainstring3 = unicode(isostring, "ISO-8859-1") 

plainstring4 = unicode(utf16string, "utf-16") 

assert plainstring1 == plainstring2 == plainstring3 == plainstring4