Python函数返回None(检查所有简单的解决方案,它们不起作用)

Question

现在,我已经编写了Python的二进制搜索(版本2.7).有时,它工作正常,但有时它会返回None,尽管搜索的值在数组中.我已经尝试了解决这个问题的每个简单方法:我已经检查了函数返回的变量是否被定义,是否执行了返回语句所在的工作流的分支.和:变量被定义,则分支被执行.

这是代码:

def binarySearch( array, desiderata, iMin, iMax ):
# Returns the index of the first instance of what we search
print 'min'
print iMin
print 'max'
print iMax

# If our search array is empty
if ( iMin > iMax ):
    return None

midP = (iMin + iMax)/2
curre = tapeNr( array[midP][TAPE_NUMBER] )
final = tapeNr( desiderata )
print 'curre'
print curre
print 'final'
print final
print 'midP'
print midP

if ( curre < final ):
    # print midP
    print "t: " + array[midP][TAPE_NUMBER] + ", d: " + desiderata
    binarySearch( array, desiderata, midP + 1, iMax )

else:
    if ( curre > final ):
        # print midP
        print "t: " + array[midP][TAPE_NUMBER] + ", d: " + desiderata
        binarySearch( array, desiderata, iMin, midP - 1 )

    else: 
        print 'hooray'
        # Now, find the first occurence of the value I need
        i = midP
        while ( array[i][TAPE_NUMBER] == desiderata ):
            i -= 1
            print i
        print (i + 1)
        return (i + 1)

由于我的调试,有很多'print'语句.最后一个,'print(i + 1)',实际打印(!)我需要的东西的索引值,但该函数仍然返回None.

你有关于问题根源的线索吗？

Answer 1

您忽略递归调用的返回值:

binarySearch( array, desiderata, midP + 1, iMax )

和

binarySearch( array, desiderata, iMin, midP - 1 )

因此,当curre < final是True:

if ( curre < final ):
    # print midP
    print "t: " + array[midP][TAPE_NUMBER] + ", d: " + desiderata
    binarySearch( array, desiderata, midP + 1, iMax )

你打电话binarySearch()后你的功能结束.如果没有显式返回,则意味着将函数返回值设置为None.

return向这些行添加语句:

return binarySearch( array, desiderata, midP + 1, iMax )

# ...

return binarySearch( array, desiderata, iMin, midP - 1 )