N嵌套for循环python

有没有什么方法像反序函数一样具有动态循环数? ['a','b','c','d'] 和 莱特迪克特是一本字典 {'a':['b','c'],'b':['a'],'c':['d'],'d':['b','c','d'] 我的代码是n=13:

for x in letters:
    for k1 in letterdict[x]:
        for k2 in letterdict[k1]:
            for k3 in letterdict[k2]:
                for k4 in letterdict[k3]:
                    for k5 in letterdict[k4]:
                        for k6 in letterdict[k5]:
                            for k7 in letterdict[k6]:
                                for k8 in letterdict[k7]:
                                    for k9 in letterdict[k8]:
                                        for k10 in letterdict[k9]:
                                            for k11 in letterdict[k10]:
                                                for k12 in letterdict[k11]:
                                                    for k13 in letterdict[k12]:
                                                        word=""
                                                        word=x+k1+k2+k3+k4+k5+k6+k7+k8+k9+k10+k11+k12+k13
                                                        print(word)

这样地:

n=3时

for x in letters:
    for k1 in letterdict[x]:
        for k2 in letterdict[k1]:
            for k3 in letterdict[k2]:
                word=""
                word=x+k1+k2+k3
                print(word)