python 按照一个字典的值来对这个字典进行排序

old_dic = {'a':6, 'b':3, 'c':2, 'd':4, 'e':5, 'f':1}
new_dic = sorted(old_dic.items(), key=lambda d:d[1])
print(new_dic)

x = zip(old_dic.values(), old_dic.keys())
y = sorted(x)
print(list(y))