Get Indexes of Negative Numbers from a List in Python
Today I was working on some code in which I had to get indexes of items in a list based on a condition. I found it interesting and thought of writing a post about a similar problem.
Here it is.
Given a list containing both positive and negative numbers, the goal is to find indexes of all negative numbers.
numbers = [1, 5, -9, -3, 0, -3]To get indexes of all negative numbers, I used the enumerate function with a condition in a list comprehension.
The enumerate function is a built-in function that returns an enumerable object. It contains pairs of indexes and values from a list.
By combining enumerate with list comprehension, I can effectively get the indexes of all negative numbers.
def find_negative_indexes(numbers):
indexes = [index for index, val in enumerate(numbers) if val < 0]
return indexesPrinting the output of find_negative_indexes method
print(find_negative_indexes(numbers))produces this output, showing a list of indexes of all negative numbers in the list.
[2, 3, 5]I also like writing tests for all my code, so here is the complete script
import unittest
def find_negative_indexes(numbers):
indexes = [i for i, n in enumerate(numbers) if n < 0]
return indexes
class TestFindNegativeIndexes(unittest.TestCase):
def test_find_negative_indexes(self):
self.assertEqual(find_negative_indexes([1, -2, 3, -4, 5]), [1, 3])
self.assertEqual(find_negative_indexes([1, 2, 3, 4, 5]), [])
self.assertEqual(find_negative_indexes([-1, -2, -3, -4, -5]), [0, 1, 2, 3, 4])
self.assertEqual(find_negative_indexes([]), [])
if __name__ == "__main__":
unittest.main()Happy Coding!