Letter Combinations of a Phone Number

LeetCode 17

class Solution:
    def letterCombinations(self, nums):
        """
        :type nums: str
        :rtype: List[str]
        """
        self.dict = {
            '1': '*',
            '2': 'abc',
            '3': 'def',
            '4': 'ghi',
            '5': 'jkl',
            '6': 'mno',
            '7': 'qprs',
            '8': 'tuv',
            '9': 'wxyz',
            '0': ' '
        }
        if not nums: return []
        self.res = []
        self.dfs(nums, "", 0)
        return self.res
    
    def dfs(self, nums, path, index):     
        if len(path) == len(nums):
            self.res.append(path)
            return
        else:
            for c in self.dict[nums[index]]:
                self.dfs(nums, path+c, index+1)