Python：IF语句中的AND运算符

Question

这是一种堆排序。

def Parent(i):
    return i / 2
def Left(i):
    return 2 * i
def Right(i):
    return 2 * i + 1

def MAX_HEAPIFY(A, i):    # A.heapSize == A[0]
    l = Left(i)
    r = Right(i)

这是问题所在。

    if l <= A[0] and A[l] > A[i]:

如果我写l <= A[0] and A[l] > A[i]，那么代码可以正确运行。 但是，如果我切换两个条件，如A[l] > A[i] and l <= A[0]，则会出现错误。 IndexError：列表索引超出范围

        largest = l
    else: largest = i
    if r <= A[0] and A[r] > A[largest]:
        largest = r
    if largest != i:
        temp = A[i]
        A[i] = A[largest]
        A[largest] = temp
        print "exchange parent %d with child %d" %(A[largest], A[i]) 
        MAX_HEAPIFY(A, largest)

def BUILD_MAX_HEAP(A):
    A[0] = len(A) - 1
    for i in range(len(A) / 2, 0, -1):
        MAX_HEAPIFY(A, i)

def HEAPSORT(A):
    BUILD_MAX_HEAP(A)
    print A
    for i in range(len(A) - 1, 1, -1):
        temp = A[1]
        A[1] = A[i]
        A[i] = temp
        A[0] = A[0] - 1   # A.heapSize - 1
        print "exchange parent %d with child %d the last" %(A[i], A[1]) 
        MAX_HEAPIFY(A, 1)

感谢您的帮助。