Non-zero elements of a list in Python

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]]

The error is

in <module>

TypeError: object of type 'bool' has no len()

The expected output is


>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

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