I have a list `J`

. I want to identify number of non-zero elements and divide by 12 and then multiply by 100. But I get an error. I present the expected output.

```
J=[[1, 4, 0, 0, 0, 9, 0]]
Percent_Unvisited=(len(J[0]!=0)/12)*100
print(Percent_Unvisited)
```

The error is

```
in <module>
Percent_Unvisited=(len(J[0]!=0)/12)*100
TypeError: object of type 'bool' has no len()
```

The expected output is

```
25
```

### >Solution :

You can use a generator expression with `sum`

to count the number of elements that are non-zero. This works because `True`

and `False`

are equivalent to `1`

and `0`

, respectively, when used in arithmetic.

```
Percent_Unvisited = sum(x != 0 for x in J[0]) / 12 * 100
```