leetcode 2194. Cells in a Range on an Excel Sheet

class Solution:
    def cellsInRange(self, s: str) -> List[str]:
        ans=[]
        s1,s2=s.split(':')
        start=ord(s1[0])
        end=ord(s2[0])
        sheetStart=int(s1[1])
        sheetEnd=int(s2[1])
        for i in range(start,end+1):
            for j in range(sheetStart,sheetEnd+1):
                ans.append(chr(i)+str(j))
        return ans