input: Write a function called primeSieve that takes an integer n as input and returns a list of all prime numbers up to n. If n is less than 2, the function should return an empty list.
  
  def primeSieve(n): 
      if n < 2:
          return []
      prime_list = [True for i in range(n+1)] 
      p = 2
      while (p * p <= n): 
          if (prime_list[p] == True): 
              for i in range(p * 2, n+1, p): 
                  prime_list[i] = False
          p += 1
      primes=[] 
      for p in range(2, n): 
          if prime_list[p]: 
              primes.append(p) 
      return primes
  
  assert primeSieve(10)==[2, 3, 5, 7]
  assert primeSieve(20)==[2, 3, 5, 7, 11, 13, 17, 19]
  assert primeSieve(1)==[]
  assert primeSieve(-1)==[]
  assert primeSieve(0)==[]
output: def primeSieve(n): 
      if n < 2:
          return []
      prime_list = [True for i in range(n+1)] 
      p = 2
      while (p * p <= n): 
          if (prime_list[p] == True): 
              for i in range(p * 2, n+1, p): 
                  prime_list[i] = False
          p += 1
      primes=[] 
      for p in range(2, n): 
          if prime_list[p]: 
              primes.append(p) 
      return primes