TypeError: 'NoneType' object is not iterable

Question

I have a function "checkAllInOneDirection" which is a recursive loop. When I break out of the loop, the function returns 1 array and 3 booleans. The weirdest thing is that within the recursive function, as it returns, it showed all of which have values yet I'm still getting the "None Type" error:

Here's the print:

Before return : [[0, 0]] False False False False

But as it returns and before it exception out, the values of returned became

    After returned : [[0, 0]] True True True True

Although the returned values out of the recursive is changed and wrong, there's still some value, yet I'm exception out of a "None Type" error? Here's the error:

     File "C:\xampp\htdocs\ZoneFinding\zoneFinder2D_V2.py", line 127, in handleCheck
    finalCatch, forBoo, bakBoo, upBoo, dwnBoo = checkAllInOneDirection(finalCatch,tempCatch,recursiveCount,newCatch, columnCount, rowCount, width, height, posToCheck, forBoo, bakBoo, upBoo, dwnBoo)
TypeError: 'NoneType' object is not iterable

Here's the function that calls the recursive "checkAllInOneDirection".

def handleCheck(newCatch, locale, subset, width, height, rowCount, columnCount, posToCheck):
    forBoo = True; bakBoo =True; upBoo=True; dwnBoo= True; lastOneInSet =0;
    while forBoo and bakBoo and upBoo and dwnBoo :
        if locale[posToCheck[0]][posToCheck[1]] == 0:
            recursiveCount = 0; tempCatch = []; finalCatch =[]
            tempCatch.append(posToCheck)
            finalCatch, forBoo, bakBoo, upBoo, dwnBoo = checkAllInOneDirection(finalCatch,tempCatch,recursiveCount,newCatch, columnCount, rowCount, width, height, posToCheck, forBoo, bakBoo, upBoo, dwnBoo)
            replaceVal(locale, finalCatch)

    return False, finalCatch

Here's the recursive function checkAllInOneDirection code.

def checkAllInOneDirection(finalCatch,tempCatch,recursiveCount,newCatch, width, height, forBoo, bakBoo, upBoo, dwnBoo):

    isItLast = checkLast(forBoo, bakBoo, upBoo, dwnBoo)
    if isItLast:
        for each in tempCatch:
            if not each in finalCatch:
                finalCatch.append(each)
        tempCatch=[]
        for each in newCatch:
            if not each in finalCatch:
                finalCatch.append(each)
        newCatch=[]
        print "Before return :", finalCatch, forBoo, bakBoo, upBoo, dwnBoo
        return finalCatch, forBoo, bakBoo, upBoo, dwnBoo

    for each in range (0, len(tempCatch)):
        posToCheck = posToCheckBak = posToCheckUp = posToCheckDwn = [tempCatch[each][0], tempCatch[each][1]]
        ### Some code to check position forward
        newPosForward = checkForward(posToCheck, width)
        if newPosForward != False:
            tempLocale = locale[newPosForward[0]][newPosForward[1]]
        elif newPosForward == False:
            tempLocale = 1
        if newPosForward != False and tempLocale ==0 and not newPosForward in finalCatch and not newPosForward in newCatch:
            forVal = locale[newPosForward[0]][newPosForward[1]]
            newCatch.append(newPosForward)
            posToCheck = newPosForward
            forBoo = True
        elif newPosForward == False and tempLocale == 1 and not newPosForward in newCatch:
            forBoo = False

        ### Some code to check position backward
        newPosBackward = checkBackward(posToCheckBak)
        if newPosBackward != False:
            tempLocale = locale[newPosBackward[0]][newPosBackward[1]]
        elif newPosBackward == False:
            tempLocale = 1    
        if newPosBackward != False and tempLocale ==0 and not newPosBackward in finalCatch and not newPosBackward in newCatch:
            forVal = locale[newPosBackward[0]][newPosBackward[1]]
            newCatch.append(newPosBackward)
            posToCheckBak = newPosBackward
            bakBoo = True
        elif newPosBackward == False and tempLocale == 1 and not newPosBackward in newCatch:
            bakBoo = False

        ### Some code to check position upward
        newPosUp = checkUpRow(posToCheckUp)
        if newPosUp != False:
            tempLocale = locale[newPosUp[0]][newPosUp[1]]
        elif newPosUp == False:
            tempLocale = 1
        if newPosUp != False and tempLocale ==0 and not newPosUp in finalCatch and not newPosUp in newCatch:
            forVal = locale[newPosUp[0]][newPosUp[1]]
            newCatch.append(newPosUp)
            posToCheckUp = newPosUp
            upBoo = True
        elif newPosUp == False and tempLocale == 1 and not newPosUp in newCatch:
            upBoo = False

        ### Some code to check position downward
        newPosDwn = checkDwnRow(posToCheckDwn, height)
        if newPosDwn != False:
            tempLocale = locale[newPosDwn[0]][newPosDwn[1]]
        elif newPosDwn == False:
            tempLocale = 1
        if newPosDwn != False and tempLocale ==0 and not newPosDwn in finalCatch and not newPosDwn in newCatch:
            forVal = locale[newPosDwn[0]][newPosDwn[1]]
            newCatch.append(newPosDwn)
            posToCheckDwn = newPosDwn
            dwnBoo = True
        elif newPosDwn == False and tempLocale == 1 and not newPosDwn in newCatch:
            dwnBoo = False

    for each in tempCatch:
        if not each in finalCatch:
            finalCatch.append(each)
    tempCatch =[]
    for each in newCatch:    
        if not each in finalCatch:
            finalCatch.append(each)
            tempCatch.append(each)
    newCatch = []

    checkAllInOneDirection(finalCatch,tempCatch,recursiveCount,newCatch, width, height, forBoo, bakBoo, upBoo, dwnBoo)

Answer 1

I think you want the last line to be:

return checkAllInOneDirection(...)

instead of just:

checkAllInOneDirection(...)

After you fall off the end of that statement, the function returns. As it has no explicit return statement, it returns None.

Answer 2

finalCatch, forBoo, bakBoo, upBoo, dwnBoo = checkAllInOneDirection(...)

expects something of the form a,b,c,d,e on the right side of the equals. This is a syntactical shortcut for a list, a tuple, or a range. If a function doesn't return, or returns something that can't be iterated over, that's the sort of error you'd expect.

Iterating means the following: suppose you have a class that acts as a container for values. Iterating over the class or over the values is to examine each value one-by-one. If you're examining a class that doesn't support that sort of behavior (e.g. integers), it'll throw an error because there's no way to handle the request.