```
class Solution(object):
def islandPerimeter(self, grid):
"""
:type grid: List[List[int]]
:rtype: int
"""
sum,x,y = 0,len(grid),len(grid[0])
for i,row in enumerate(grid):
for j,item in enumerate(row):
sum += 4 - 2*((grid[i + 1][j] if i < x - 1 else 0) + (grid[i][j + 1] if j < y - 1 else 0)) if item else 0
return sum
```