So I’m currently learning Python and I came across a problem with a None value. I’am asking myself what does it mean in the context of the short program and is there any way to visualize it?

list = eval(input("Enter a list with positive numbers: "))
n = len(list)
i = 0
*previous = None*
erg = []
while i < n:
    current = list[i]
    i += 1
    *if current == previous:*
        continue
    if current <= 0:
        print("Negative number found!")
        break
    erg.append(current)
    previous = current

print(erg)

The lines I don’t understand are in Italic. So is the line current == previous just checking if there is a value at all or not and positive values get left out in the while-loop?