如何遍歷類的所有實例？

Question

因此，我知道以前已經有人問過這個問題，但是我找不到我的問題的答案，所有的答案都讓我更加困惑。

因此，我創建了一個名為Books的類，該類將文件的位置和文件名作為輸入，並具有一種稱為countwords的方法，該方法可對文件的單詞進行計數。

我創建了此類的一堆實例（它們被稱為嗎？），但我不想在所有實例上迭代CountWords方法。 這是我的代碼：

class Books():
    def __init__(self, path, fullname):
        self.path     = path
        self.fullname = fullname

    def count_words(self):
        try:
            with open(self.path + self.fullname, encoding='utf-8') as f:
                contents = f.read()
        except FileNotFoundError:
            print(f"Sorry, the file {self.fullname} doesn't exist.")
        else:
            words     = contents.split()
            num_words = len(words)
            print(f"The file {self.fullname} has about {num_words}" 
                  f"words.")             

alice        = Books("text_files/", 'alice.txt')
siddharta    = Books("text_files/", 'siddhartha.txt')
mobydick     = Books('text_files/', 'moby_dick.txt')
little_women = Books('text_files/', 'little_women.txt')

我不會寫這樣的東西：

for book in Books.list():
    book.count_words()

並得到：

 The file alice.txt has about 29465 words. 
 The file siddhartha.txt has about 1500 words.
 The file moby_dick.txt has about 215830 words. 
 The file little_women.txt has about 189079 words. 

打印與Books（）類關聯的所有實例的單詞計數，如何實現呢？ 謝謝！

編輯 ：我嘗試了不同的方法，但這是我現在正在使用的一種：

1. 第一個是導入weakref（不知道這是做什么的）。

2. 然后在課程開始時添加一個空列表。

3. 之后，使用：def init末尾的self .__ class__LISTNAME_append（weakref.proxy（self））

4. 然后，您可以遍歷LISTNAME。

碼：

# 1 
import weakref

class Book():
  # 2
  book_list = []
  def __init__(self, path, fullname):
      self.path = path
      self.fullname = fullname
      # 3
      self.__class__.book_list.append(weakref.proxy(self))

  def count_words(self):
      try:
          with open(self.path + self.fullname, encoding='utf-8') as f:
              contents = f.read()
      except FileNotFoundError:
          print(f"Sorry, the file {self.fullname} doesn't exist.")
      else:
          words = contents.split()
          num_words = len(words)
          print(f"The file {self.fullname} has about {num_words} "
                f"words. ")

alice = Book("text_files/", 'alice.txt')

siddharta = Book("text_files/", 'siddhartha.txt')

mobydick = Book('text_files/', 'moby_dick.txt')

little_women = Book('text_files/', 'little_women.txt')

# 4
for book in Book.book_list:
  book.count_words()

Answer 1

而不是你的類繼續引用已創建的所有情況下，我建議你先定義你的數據，然后創建從數據實例的集合。

例如：

book_paths = [('text_files/', 'alice.txt'),
              ('text_files/', 'siddharta.txt'),
              ('text_files/', 'moby_dick.txt'),
              ('text_files/', 'little_women.txt')]

books = []

for path, name in book_paths:
    book = Books(path, name)
    books.append(book)
    book.count_words()

您還可以稍后遍歷books以執行所需的任何操作。 使用list推導的另一種方法：

books = [Books(path, name) for path, name in book_paths]

for book in books:
    book.count_words()

Answer 2

您要做的就是創建一個類變量，該變量將在實例化實例時存儲書籍信息。

然后公開一個類級別的方法，該方法將在調用Books.list時返回此列表。

這是相同的代碼

class Books(object):

  _books_list = list() 

    def __init__(self, path, fullname):
        self.path = path
        self.fullname = fullname
        self._books_list.append(self.path + self.fullname)

    def count_words(self):
        try:
            with open(self.path + self.fullname, encoding='utf-8') as f:
                contents = f.read()
        except FileNotFoundError:
            print(f"Sorry, the file {self.fullname} doesn't exist.")
        else:
            words = contents.split()
            num_words = len(words)
            print(f"The file {self.fullname} has about {num_words}"
                  f"words.")

  @classmethod def list(): return self._books_list 

alice = Books("text_files/", 'alice.txt')
siddharta = Books("text_files/", 'siddhartha.txt')
mobydick = Books('text_files/', 'moby_dick.txt')
little_women = Books('text_files/', 'little_women.txt')

Answer 3

那是解決問題的錯誤方法。

我建議您改為創建一個類字典，以文件名作為鍵：

代替：

alice = Books("text_files/", 'alice.txt')
siddharta = Books("text_files/", 'siddhartha.txt')
mobydick = Books('text_files/', 'moby_dick.txt')
little_women = Books('text_files/', 'little_women.txt')

做：

books_dict = {name:Books('text_files/',name+".txt") for name in ["alice","siddhartha","moby_dick","little_women"}

現在，您有了一個Books實例的字典。 您現在可以像這樣迭代它：

for book_name,book_instance in books_dict.items():
    print(book_name,book_instance)

如果要“注銷”實例，請執行以下操作：

books_dict.pop("alice")

最好不要為x個實例創建x個變量。 使用聯合結構。

Answer 4

從您的變量來看，通過命名Book類可能更容易理解：

class Book():
    def __init__(self, path, fullname):
        self.path = path
        self.fullname = fullname

    def count_words(self):
        try:
            with open(self.path + self.fullname, encoding='utf-8') as f:
                contents = f.read()
        except FileNotFoundError:
            print(f"Sorry, the file {self.fullname} doesn't exist.")
        else:
            words = contents.split()
            num_words = len(words)
            print(f"The file {self.fullname} has about {num_words}" 
                  f"words.")    

按照您的描述制作書籍實例

alice = Book("text_files/", 'alice.txt')
siddharta = Book("text_files/", 'siddhartha.txt')
mobydick = Book('text_files/', 'moby_dick.txt')
little_women = Book('text_files/', 'little_women.txt')

並將它們添加到被稱為books的列表中：

books = [alice, siddhartha, mobydick, little_women]

然后您可以遍歷列表，在每本書上調用count_words方法