python - make a value zero if exception list index out of range -

i'm doing calculation in python , have sum items list, if on list. code:

ei=-j*s[i][j]*(s[i+1][j]+s[i-1][j]+s[i][j+1]+s[i][j-1])

what want make 0 value of element gives error list index out of range. there way without verifying if every element of sum exists?

thanks in advance

edit

i don't want sum 0, element gives error

you write function using try/except

def get_value(s, i, j):     try:         return s[i][j]     except indexerror:         return 0

then use it

 ei = -j * get_value(s, i, j) * (get_value(s, i+1, j) + get_value(s, i-1, j) +get_value(s, i, j+1) + get_value(s, i, j-1))

Script