無法將列表作爲類屬性

Question

我已經創建了一個迭代器。我試圖通過配方成分迭代來檢查純素食者是否可以。

class Vegan: 

    NONE_VEGAN_INGREDIENT = ['egg', 'milk', 'honey', 'butter'] 

    def __init__(self, *args): 
     self.ingredient_list = (args) 
     self.index = -1 

    def __iter__(self): 
     return self 

    def __next__(self): 
     if self.index == len(self.ingredient_list): 
      raise StopIteration 
     for ingredient in self.ingredient_list: 
      if ingredient in Vegan.NONE_VEGAN_INGREDIENT: 
       self.index += 1 
       return ('{} is a vegan ingredient'.format(ingredient[self.index])) 
      else: 
       self.index += 1 
       return ('{} is NOT a vegan ingredient'.format(ingredient[self.index])) 

iterable = Vegan('tomato', 'banana', 'asd', 'egg', 'tomato') 
iterator = iter(iterable) 
while True: 
    try: 
     print(next(iterator)) 
    except StopIteration: 
     break 

，你可以看到，我路過*指定參數時，這應該是一個名單，但每當我嘗試運行此，它通過第一個字迭代，並檢查單詞「番茄」的信。我想讓我的迭代器遍歷所有的成分，如果某些東西不在NONE_VEGAN_INGREDIENT列表中，那麼就按原樣打印在代碼中。我怎樣才能通過一個列表？

Answer 1

您的問題得到解決是因爲你索引的元素不是元組，ingredient[self.index]應該是self.ingredient_list[self.index]。

您可以簡化代碼通過使表現得像你的，但工作ARGS迭代這樣你就可以通過字符串作爲你無需將它們放在一個列表等：

class Vegan: 
    NONE_VEGAN_INGREDIENT = ['egg', 'milk', 'honey', 'butter'] 

    def __init__(self, *args): 
     self.ingredient_iter = iter(args) 
    def __iter__(self): 
     return self 

    def __next__(self): 
     ingredient = next(self.ingredient_iter) 
     if ingredient in Vegan.NONE_VEGAN_INGREDIENT: 
      return '{} is a vegan ingredient'.format(ingredient) 
     return '{} is NOT a vegan ingredient'.format(ingredient) 


iterable = Vegan('tomato', 'banana', 'asd', 'egg', 'tomato') 

for ele in iterable: 
    print(ele) 

輸出：

In [2]: iterable = Vegan('tomato', 'banana', 'asd', 'egg', 'tomato') 

In [3]: for ele in iterable: 
    ...:   print(ele) 
    ...:  
tomato is NOT a vegan ingredient 
banana is NOT a vegan ingredient 
asd is NOT a vegan ingredient 
egg is a vegan ingredient 
tomato is NOT a vegan ingredient 

你提高自己的代碼一個StopIteration但調用next(iterable)會做相同的，所以，使得對象的點迭代是你能所迭代直接在它上面，所以不需要嘗試/除外。也我通過參數，這應該是一個列表是不正確的，參數是一個元組。

此外，如果你有很多成分的檢查使NONE_VEGAN_INGREDIENT一組會更有效：

NONE_VEGAN_INGREDIENT = {'egg', 'milk', 'honey', 'butter'} 

Answer 2

這裏是一個可能的解決問題的方法：

class Vegan: 

    NONE_VEGAN_INGREDIENT = ['egg', 'milk', 'honey', 'butter'] 

    def __init__(self, *args): 
     self.ingredient_list = (args) 

    def __iter__(self): 
     self.index = 0 
     return self 

    def __next__(self): 
     if self.index >= len(self.ingredient_list): 
      raise StopIteration 

     ingredient = self.ingredient_list[self.index] 
     self.index += 1 

     if ingredient in Vegan.NONE_VEGAN_INGREDIENT: 
      return ('{} is a vegan ingredient'.format(ingredient)) 
     else: 
      return ('{} is NOT a vegan ingredient'.format(ingredient)) 

iterable = Vegan('tomato', 'banana', 'asd', 'egg', 'tomato') 
iterator = iter(iterable) 

while True: 
    try: 
     print(next(iterator)) 
    except StopIteration: 
     break 

在任何情況下，我覺得這個問題可能在1個或2行，而不是使用__iter__和__next__方法，這樣

Answer 3

我覺得跟你的類問題是，你通過你的__next__()方法的元素循環。下面是使用代碼的解決方案：

class Vegan: 

    NONE_VEGAN_INGREDIENT = ['egg', 'milk', 'honey', 'butter'] 

    def __init__(self, *args): 
     self.ingredient_list = args 
     self.index = -1 

    def __iter__(self): 
     return self 

    def __next__(self): 
     if self.index == len(self.ingredient_list) - 1: # index is incremented 
      raise StopIteration 
     self.index += 1 
     if self.ingredient_list[self.index] in Vegan.NONE_VEGAN_INGREDIENT: 
      return ('{} is a vegan ingredient'.format(self.ingredient_list[self.index])) 
     else: 
      return ('{} is NOT a vegan ingredient'.format(self.ingredient_list[self.index])) 

iterable = Vegan('tomato', 'banana', 'asd', 'egg', 'tomato') 
iterator = iter(iterable) 
while True: 
    try: 
     print(next(iterator)) 
    except StopIteration: 
     break 

我所做的只是改變指數檢查出界len() - 1和刪除的for循環。這工作，產生輸出我假設你所追求的：

tomato is NOT a vegan ingredient 
banana is NOT a vegan ingredient 
asd is NOT a vegan ingredient 
egg is a vegan ingredient 
tomato is NOT a vegan ingredient 

編輯：用if語句