Pythonic代码将3位数字转换为所有可能的字母组合

Question

给一个字典，其中1：a，2：b ... 26：z。我需要找到可以由三个数字组成的所有可能的字母组合。

所有数字都应在末尾用完。每个数字应该单独翻译为一个字母，或者我可以组合相邻的数字来检查一个字母。例如-

121转换为aba，au，la;

151转换为ea，oa;

101转换为ja;

我能够使它工作，但是我觉得我的代码不是很“ pythonic”。我正在尝试找出一个更有效和类似Python的解决方案。

# creating the dict that has keys as digits and values as letters
root_dict = {}
for num in range(0,26):
    root_dict[str(num+1)] = string.ascii_lowercase[num]

# asking user for a three digit number
sequence_to_convert = raw_input('Enter three digit number \n')

# storing all possible permutations from the three digit number
first_permutation = sequence_to_convert[0]
second_permutation = sequence_to_convert[1]
third_permutation = sequence_to_convert[2]
fourth_permutation = sequence_to_convert[0]+sequence_to_convert[1]
fifth_permutation = sequence_to_convert[1]+sequence_to_convert[2]

# checking if the permutations exist in the dict, if so print corresponding letters
if first_permutation in root_dict and second_permutation in root_dict and third_permutation in root_dict:
    print root_dict[first_permutation]+root_dict[second_permutation]+root_dict[third_permutation]
if first_permutation in root_dict and fifth_permutation in root_dict:
    print root_dict[first_permutation]+root_dict[fifth_permutation]
if fourth_permutation in root_dict and third_permutation in root_dict:
    print root_dict[fourth_permutation]+root_dict[third_permutation]