min() arg is an empty sequence

Question

I'm trying to find minimum element in matrix row, but there are two conditions: 1) it must be > 0 2) and this point must be not visited(is_visited[k] is False) I'm trying to do next:

min(x for x in matr_sum[i] if x > 0  if is_visited[k] is False )

But there is an error: min() arg is an empty sequence

The full block of code:

for k in range(4):
        if matr_sum[i][k] == min(x for x in matr_sum[i] if x > 0  if is_visited[k] is False ) and i!=k:
            return k

How to resolve it? Or should I write my min() function? Because it works with one condition:

min(x for x in matr_sum[i] if x > 0)

But with two conditions, it doesn't work.

Answer 1

If you want to avoid this ValueError in general, you can set a default argument to min(), that will be returned in case of an empty list. See described here.

min([], default="EMPTY")
# returns EMPTY

Note that this only works in Python 3.4+