why the results aren't the same ?

Question

lst =[1,-2,3,-4]
for num in lst:
if num>0 :
num = 0
print( lst )
.........
lst = [ 1, -2, 3, -4]
for i in range(len(lst)):
if lst [i] >0:
lst[i] = 0
print(lst)

Answer 1

The first code does not change anything from the list.
num is a variable on its own, which might be changed in the if-branch, but it's not connected to the list, so no effect

Answer 2

thanks;)