Here's my solution considering already in list primes:
def prastevila(n):
p = []
for k in range(2, n + 1):
i = 0
while i < len(p) and k % p[i] != 0:
i += 1
if i == len(p):
p.append(k)
return p
#In [2]: prastevila(20)
#Out[2]: [2, 3, 5, 7, 11, 13, 17, 19]