Python函数返回None（所有平凡解检查，他们不工作） [英] Python function returns None (all trivial solutions checked and they do not work)

问题描述

现在，我已经写为Python（2.7版）的二进制搜索。有时，它工作得很好，但在其他时候，它虽然搜索值是数组中返回无。我试图解决这个的每一个微不足道的方式：我已经检查了函数返回变量是否已定义，是否执行其中return语句所在的工作流的分支。和：变量的是的规定，分公司的是的执行。

Now, I have written a binary search for Python (version 2.7). Sometimes, it works just fine, but at other times it returns None although the searched value is in the array. I have tried every trivial way of fixing this: I have checked whether the variable the function returns is defined, whether the branch of the workflow in which the return statement is located is executed. And: the variable is defined, the branch is executed.

下面是code：

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)

有很多，因为我的调试打印语句。
最后他们，打印（1 + 1）'，实际打印（！）我需要的东西的索引值，但功能还是返回N​​one。

There are a lot of 'print' statements because of my debugging. The last of them, 'print (i+1)', actually prints (!) the index value of the thing I need, but the function still returns None.

你有一个关于这个问题的根源线索？

Do you have a clue about the source of the problem?

推荐答案

您忽略的返回值的递归的要求：

You ignore the return value of recursive calls:

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

和

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

所以，当真正水流＆LT;最后是真：

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

您拨打的binarySearch（）之后，你的函数结束。如果没有一个明确的回报率，这意味着你的函数的返回值设置为无代替。

you call binarySearch() after which your function ends. Without an explicit return that means your function return value is set to None instead.

添加收益语句这些行：

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

# ...

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

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