can anyone explain me that why this code will print 6

Question

def func(x):
res = 0
for i in range(x):
res += i
return res

print(func(4))

Answer 1

You are using Range(4) so loop will run for the value of i=0, i=1, i=2 and i=3
you are using same variable res to store every time.
so
res= 0+1+2+3
that's why returning 6.

Answer 2

# if in doubt of how things work try adding print statements
# at each stage to see how values are changing
def func(x):
res = 0
for i in range(x):
res += i
print('i value = ',i,'new res value = ',res)
print('loop complete final res value =',res)
return res

print('returned vale of res = ',func(4))