局部變量在Python賦值之前引用3.2

Question

原始代碼：

>>> def calcItemsLowShelfLife(shelfLifeList): 
    ctLowShelfLife = 0 
    for number in shelfLifeList: 
     if number <= 7: 
      ctLowShelfLife += 1 
    return ctLowShelfLife 
>>> shelfLifeList = [5, 7, 10] 
>>> lowShelfLife = calcItemsLowShelfLife(shelfLife) 

當我試圖運行python 3.2給我的錯誤：

Traceback (most recent call last): 
    File "<pyshell#6>", line 1, in <module> 
    lowShelfLife = calcItemsLowShelfLife(shelfLife) 
    File "<pyshell#5>", line 3, in calcItemsLowShelfLife 
    for number in shelfLifeList: 
TypeError: 'int' object is not iterable 

Answer 1

在循環開始之前，您應該聲明變量ctLowShelfLife =0。

UPDATE

問題是與您的壓痕。 您的代碼應該是這樣的，

>>> def calcItemsLowShelfLife(shelfLifeList): 
    ctLowShelfLife = 0 
    for number in shelfLifeList: 
     if number <= 7: 
      ctLowShelfLife += 1 
    return ctLowShelfLife 

>>> shelfLifeList = [5, 7, 10] 
>>> lowShelfLife = calcItemsLowShelfLife(shelfLifeList) 
>>> lowShelfLife 
2 
>>> 

Answer 2

需要初始化變量使+= 1前：

ctLowShelfLife = 0  

def calcItemsLowShelfLife(shelfLifeList): 
    global ctLowShelfLife 
    for number in shelfLifeList: 
     if number <= 7: 
      ctLowShelfLife += 1 
    return ctLowShelfLife 

shelfLifeList = [5, 7, 10] 
lowShelfLife = calcItemsLowShelfLife(shelfLifeList) 
print(lowShelfLife) 

如果您聲明ctLowShelfLife爲全球性，告訴函數你想使用全局變量。

如果你不想使用全局，你可以把它想：

def calcItemsLowShelfLife(shelfLifeList): 
    ctLowShelfLife = 0 
    for number in shelfLifeList: 
     if number <= 7: 
      ctLowShelfLife += 1 
    return ctLowShelfLife 

shelfLifeList = [5, 7, 10] 
lowShelfLife = calcItemsLowShelfLife(shelfLifeList) 
print(lowShelfLife)