Python 类对象出现在for循环的if和else语句下为什么？

为什么带有option=“first”的类对象出现在列表

btest

和列表

ctest

中

我在一段较大的代码中遇到了这个问题，所以我编写了这段较小的代码，以便更好地理解if/else语句如何在类对象列表的for循环中工作。但我还是不明白

class test:
   def __init__(self,option,place):
       self.option=option
       self.place=place

   def __repr__(self):
       return("option:"+self.option+"\npalce:"+self.place)


optionlist=["first","second","thrid","fourth"]
placelist=["switzerland","germany","thailand","italy"]
testlist=[]

item=0
while item <len(optionlist):
   testl=test(optionlist[item],placelist[item])
   testlist.append(testl)
   item+=1

btest=[]
ctest=[]

for x in testlist:
    if x.option=="first":
       btest.append(x)
       print("here")       
    if x.option=="second": 
        print("here2") 

        # If I delete this 2nd if statement the ctest list
        # doesn't contain a object with option="first", but if I
        # leave it it does. Why?
    else:
        ctest.append(x)
        print("no")

print("btest:",btest)
print("ctest:",ctest)

这也是我所期望的，但是如果我让它用第二条if语句运行，为什么它会给出以下输出：

here
no
here2
no
no
btest: [option:first
palce:switzerland]
ctest: [option:first
palce:switzerland, option:thrid
palce:thailand, option:fourth
palce:italy]

---

因为它是两个不同的

if

语句。 看起来您需要使用

if/elif/else

：

    if x.option=="first":
       btest.append(x)
       print("here")       
    elif x.option=="second": 
        print("here2") 

        # If I delete this 2nd if statement the ctest list
        # doesn't contain a object with option="first", but if I
        # leave it it does. Why?
    else:
        ctest.append(x)
        print("no")

---

因为你把它编码成这样：

if x.option=="first": 
   btest.append(x)               # when x.option == "first" add to btest
   print("here")       

if x.option=="second": 
    print("here2") 
else:
    ctest.append(x)              # when x.option NOT "second" add to ctest
    print("no")                  #      x.option == "first" is NOT second - so added

您可以将其更改为if:elif:else:。。。然后，

second

将永远不会添加到任何内容中，因为它只打印

s

if x.option=="first": 
   btest.append(x)               # when x.option == "first" add to btest
   print("here")       

if x.option=="second": 
    print("here2") 
else:
    ctest.append(x)              # when x.option NOT "second" add to ctest
    print("no")                  #      x.option == "first" is NOT second - so added