decimal point trimming

This seems like a bug to me, but it could be me. It seems like my decimal points are being lopped off when I attempt to return a float value (as seen in the return float(12.5) below.

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):

    srt = sorted(data)
    l = len(data)

    print (srt)

    if l % 2 == 1:
        return srt[l // 2]
    else:
        print (srt[l // 2] , "+", srt[l // 2 - 1])
        x = srt[(l // 2)]
        y = srt[(l // 2 - 1)]

        if (x + y)//2.0 == 12.5:
            **return float(12.5)**
        return (x + y)//2.0

    #replace this for solution
    return 'ERROR'

#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.")