[LeetCode&Python] Problem 784. Letter Case Permutation

Given a string S, we can transform every letter individually to be lowercase or uppercase to create another string.  Return a list of all possible strings we could create.

Examples:
Input: S = "a1b2"
Output: ["a1b2", "a1B2", "A1b2", "A1B2"]

Input: S = "3z4"
Output: ["3z4", "3Z4"]

Input: S = "12345"
Output: ["12345"]

Note:

• S will be a string with length between 1 and 12.
• S will consist only of letters or digits.

import itertools
class Solution(object):
    def letterCasePermutation(self, S):
        """
        :type S: str
        :rtype: List[str]
        """
        L=[[i.upper(),i.lower()] if i.isalpha() else i for i in S]
        return [''.join(i) for i in itertools.product(*L)]