Product of Odd elements in array

def arrayOddProduct(arr):
    """Returns a product of odd elements in array arr."""
    s = 1
    for a in arr:
        if ??: # REPLACE ??
          s *= a
    return s

if __name__ == "__main__":
    arr = [1,2,3,4,5,6,7]
    result = arrayOddProduct(arr)
    expected = 105
    assert result == expected, ("product of array %s must be %d, but it is %d" % (arr, expected, result))