why the answer is 8?

Question

for i in range (5):
i += i
print (i)

Answer 1

'i' is a temporary variable, each iteration replaced by the next value from the itearable range(5) so last value 4 is replaced by previous value and it's i+=i cause it's value 4+4=8 , it is retained after loop and it printed.

Try to test printing inside loop then you can see each values...
Hope it helps...

Answer 2

Indent the third line (the print (i) statement) and see how the output works:

for i in range (5):
i += i
print (i)