Letter Combination of a phone number

'''
Time complexity = (k^n)*n where k=max count of all the chars for each digit ie.4 for 7='pqrs' and n for string building for all the chars.
'''

def fun(num,cur,i,ans):
    if i>=len(num) and cur!="":
        ans.append(cur)
        return

    dict={"2":"abc","3":"def","4":"ghi","5":"jkl",'6':"mno","7":"pqrs","8":"tuv","9":"wxyz"}
    current_num=num[i]
    val=dict[current_num]
    print(current_num,cur)
    for k in val:
        fun(num,cur+k,i+1,ans)

class Solution:
    def letterCombinations(self, num: str) -> List[str]:
        ans=[]
        fun(str(num),"",0,ans)
        return ans