Added Python solution for "Single Number"

Author: Kyrylo-Ktl

Python/Single Number.py

@@ -0,0 +1,13 @@
+from functools import reduce
+from operator import xor
+from typing import List
+
+
+class Solution:
+    """
+    Time:   O(n)
+    Memory: O(1)
+    """
+
+    def singleNumber(self, nums: List[int]) -> int:
+        return reduce(xor, nums)