Project Euler problems 1 and 2 in python
Problem 1 is probably better and more pythonic when written as a list comprehension:

x = sum(i for i in range(1000) if i % 3 == 0 or i % 5 == 0)
print(x)


For the second problem I would recommend a generator and to use sum again:

def fibonacci(max_n):
    n, prev = 1, 1
    while n &lt;= max_n:
        yield n
        n, prev = n + prev, n

total = sum(n for n in fibonacci(4000000) if n % 2 == 0)
print(total)


This way only two ints are ever in memory (well three if you count max_n). In comparison, your code has a list of possibly large size.