PhoneNumToLetter.py

'''
Given a digit string, 
return all possible letter combinations that the number could represent.

A mapping of digit to letters
(just like on the telephone buttons) is given below.
1 2abc 3def
4ghi 5jkl 6mno
7pqrs 8tuv 9wxyz
 * 0 #

Input:Digit string "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
'''
phone_map = {
 2:'abc',
 3:'def',
 4:'ghi',
 5:'jkl',
 6:'mno',
 7:'pqrs',
 8:'tuv',
 9:'wxyz'
}

def letter_combination(str1):
 letters = []
 for char in str1:
 if phone_map[char]:
 letters.append(list(phone_map[char])