为什么我的 python while 循环停止？

Question

I've got a loop that is supposed to select features and keep looping until it is no longer selecting new features

arcpy.SelectLayerByLocation_management("antiRivStart","INTERSECT","polygon")

previousselectcount = -1
selectcount = arcpy.GetCount_management("StreamT_StreamO1")
while True:
#selectCount = arcpy.GetCount_management("StreamT_StreamO1")
    mylist = []
    with arcpy.da.SearchCursor("antiRivStart","ORIG_FID") as mycursor:
        for feat in mycursor:
            mylist.append(feat[0])
            liststring = str(mylist)
            queryIn1 = liststring.replace('[','(')
            queryIn2 = queryIn1.replace(']',')')
    arcpy.SelectLayerByAttribute_management('StreamT_StreamO1',"ADD_TO_SELECTION",'OBJECTID IN '+ queryIn2 )
    arcpy.SelectLayerByLocation_management("antiRivStart","INTERSECT","StreamT_StreamO1","","ADD_TO_SELECTION")
    previousselectcount = selectcount
    selectcount = arcpy.GetCount_management("StreamT_StreamO1")
    print str(selectcount), str(previousselectcount)
    if selectcount == previousselectcount:
        break

By my reckoning, once it starts print the name number twice it should stop, but it doesn't, its keeps print "15548 15548" over and over again. Is it ingnoring the break or is the if condition not being met?

I've also tried with

while selectcount != previousselectcount:

but this gave me the same result

Answer 1

Variables in Python are dynamic. Just because you initialise previousselectcount as an integer doesn't mean it will be one when you call previousselectcount = selectcount . You can feel free to get rid of that line.

If you replace:

selectcount = arcpy.GetCount_management("StreamT_StreamO1")

With:

selectcount = int(arcpy.GetCount_management("StreamT_StreamO1").getOutput(0))

For both lines you'll be comparing the integer values instead of whatever the equality operator is comparing for the object.

Even better, why not write a function to do it for you:

def GetCount():
    return int(arcpy.GetCount_management("StreamT_StreamO1").getOutput(0))

Save yourself repeating yourself.