Python随机unicode字符串

Question

我是python和unicode的新手。我试图在python中生成一个随机的unicode字符串。这就是我想出的：

def randomUnicodeStr(self, ustart, uend):
    '''Generate a random unicode string whose length is strlen and whose unicode characters are in range ustart, uend'''
    strlen = 5
    uchars = [random.choice(range(ustart, uend+1)) for _ in range (strlen)]
    ustr   = u''
    for uc in uchars:
        ustr += unichr(uc)

    #for i in range(len(ustr)):
    #    print "Py char " + str(i) + " = " + str(ord(ustr[i]))

    return ustr

我无法从python文档中收集此信息，但上面的ustr使用了哪种编码？