Python: Can any one explain this while loop.

This seems like an easy one. My doubt is, when is "num" changing its value.


def nearest_square(limit):
num = 0
while (num+1)**2 < limit:

print(num)
num += 1
print(num)
retu num**2


limit = 20
print(nearest_square(limit))

OUTPUT:
0
1
2
3
16


In the code I am incrementing "num" twice. (Once in the condition of while loop and second inside the while loop)