Code works on native interpreter

I would like to give some feedback about ...

From: http://www.checkio.org/mission/median/solve/

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My Code:

def checkio(data):
    data.sort()
    length = len(data)
    median = None
    if length % 2:
        # Odd len
        median = data[int(length/2)]
    else:
        # Even len
        median = (data[(length/2) - 1] + data[length/2])/2

    #replace this for solution
    return median

#These "asserts" using only for self-checking and not necessary for auto-testing
if __name__ == '__main__':
    assert checkio([1, 2, 3, 4, 5]) == 3, "Sorted list"
    assert checkio([3, 1, 2, 5, 3]) == 3, "Not sorted list"
    assert checkio([1, 300, 2, 200, 1]) == 2, "It's not an average"
    assert checkio([3, 6, 20, 99, 10, 15]) == 12.5, "Even length"
    print("Start the long test")
    assert checkio(list(range(1000000))) == 499999.5, "Long."
    print("The local tests are done.")