chop.py

def chop(target, search_array):
  if target in search_array:
    return search_array.index(target)
  else:
    return -1

test_chop.py

from chop import chop
import unittest

class TestSequenceFunctions(unittest.TestCase):

  def test_chop(self):
    self.assertEqual(-1, chop(3, []))
    self.assertEqual(-1, chop(3, [1]))
    self.assertEqual(0,  chop(1, [1]))
#
    self.assertEqual(0,  chop(1, [1, 3, 5]))
    self.assertEqual(1,  chop(3, [1, 3, 5]))
    self.assertEqual(2,  chop(5, [1, 3, 5]))
    self.assertEqual(-1, chop(0, [1, 3, 5]))
    self.assertEqual(-1, chop(2, [1, 3, 5]))
    self.assertEqual(-1, chop(4, [1, 3, 5]))
    self.assertEqual(-1, chop(6, [1, 3, 5]))
#
    self.assertEqual(0,  chop(1, [1, 3, 5, 7]))
    self.assertEqual(1,  chop(3, [1, 3, 5, 7]))
    self.assertEqual(2,  chop(5, [1, 3, 5, 7]))
    self.assertEqual(3,  chop(7, [1, 3, 5, 7]))
    self.assertEqual(-1, chop(0, [1, 3, 5, 7]))
    self.assertEqual(-1, chop(2, [1, 3, 5, 7]))
    self.assertEqual(-1, chop(4, [1, 3, 5, 7]))
    self.assertEqual(-1, chop(6, [1, 3, 5, 7]))
    self.assertEqual(-1, chop(8, [1, 3, 5, 7]))

if __name__ == '__main__':
  unittest.main()