Saved from https://stackoverflow.com/questions/68884998/python-lowest-missing-integer-codility-demo-task-what-am-i-missing

test_codility.py

def solution(A):
  #Get rid of all zero and negative #'s
  A = [i for i in A if i > 0]
  #At this point, if there were only zero, negative, or combination of both, the answer is 1
  if (len(A) == 0): return 1
  count = 1
  #Get rid of repeating values
  A = set(A) 
  #At this point, we may have only had the same # repeated. 
  #If repeated 1's answer is 2
  #If any other repeated #'s only, then answer is 1
  if (len(A) == 1):
      if (list(A)[0] == 1):
          return 2
      else:
          return 1
  #Sort the array
  A = sorted(A)
  for j in range(len(A)):
      #Test to see if it's >= to count. If so, it exists and is not the lowest integer.
      if (A[j] <= count): #If the number is lt or equal to the count then continue the count
              count = count + 1
      else: 
           return count 
  return count