# \_\_abstractmethods\_\_, get\_cache\_token, update\_abstractmethods ## \_\_abstractmethods\_\_ *** 是一個維護系統的屬性，包含必須由 abstract base class 的具體子類別實現的抽象方法和屬性的名稱。 當使用 `abc` module 定義 abstract base class 時，任何用 `@abstractmethod` 修飾的方法都會加入到 `__abstractmethods__` set 中。除非覆寫其所有抽象方法，否則無法實例化從 abstract base class 繼承的類別。 **Example: Basic usage** {% code title="PYTHON" %} ```python import abc class ElectronicDevice(abc.ABC): @abc.abstractmethod def turn_on(self): pass @abc.abstractmethod def turn_off(self): pass @property @abc.abstractmethod def is_on(self): pass class Television(ElectronicDevice): def __init__(self): self._is_on = False def turn_on(self): if not self._is_on: self._is_on = True print("Television is now ON.") def turn_off(self): if self._is_on: self._is_on = False print("Television is now OFF.") @property def is_on(self): return self._is_on print(ElectronicDevice.__abstractmethods__) # Output: frozenset({'turn_on', 'turn_off', 'is_on'}) print(Television.__abstractmethods__) # Output: frozenset() ``` {% endcode %} ## get\_cache\_token() *** 提供了一個 token，每次透過 `register()` 修改ABC時，該 token 都會更改。此 token 對於 caching 和追蹤 ABC registry 的變更很有用。 它返回一個不透明的物件 (意味著用戶無法直接理解或使用其內部結構)，用於標記 Virtual subclass cache 的版本。 該物件支援相等性測試，因此可以用來檢查 cache 是否已經更改。 {% code title="PYTHON" %} ```python abc.get_cache_token() ``` {% endcode %} {% hint style="info" %} **每次在調用 `register()` 時，cache token 都會發生變化。 這意味著當您註冊 Virtual subclass cache 時，cache token 將會更改。** Cache token 是一種版本控制的機制。 {% endhint %} {% hint style="warning" %} **它主要用於處理大型 Class 層次結構，並且需要確保正確傳遞 Abstract Class 中的更改的情況。大多數 Python 開發人員可能永遠不需要使用 `get_cache_token()`。** {% endhint %} **Example: Basic usage** {% code title="" %} ```python import abc from abc import ABC class MyABC(ABC): pass cache_token = abc.get_cache_token() print(cache_token) # Output: 37 # Function to demonstrate cache token usage def is_abc_up_to_date(cache_token): current_token = abc.get_cache_token() return current_token == cache_token print("ABC registry updated:", not is_abc_up_to_date(cache_token)) # Output: False @MyABC.register class MyConcreteClass: pass print("ABC registry updated:", not is_abc_up_to_date(cache_token)) # Output: True ``` {% endcode %} ## update\_abstractmethods() *** 用於重新計算 Abstract class 的抽象狀態，在建立 Class 後加入或實現 abstract 方法的情況下非常有用。 如果沒有使用 `update_abstractmethods(cls)`，Python 不會自動重新計算的 abstract 方法。 {% code title="PYTHON" %} ```python abc.update_abstractmethods(cls) ``` {% endcode %} {% hint style="info" %} **在 Abstract class 已經定義之後，您不能動態地加入新的 abstract 方法。 僅能使用 `update_abstractmethods()` 。** {% endhint %} {% hint style="info" %} **`update_abstractmethods()` 並不常用。用例涉及動態行為，這在傳統的 Python 應用程式中並不常見。它更常見於進行大量 meta-programming 的 rameworks or libraries 中。** {% endhint %} {% hint style="warning" %} **頻繁使用此函數會使程式碼更難以理解和維護。通常最好對 class 層次結構有一個清晰、靜態的定義。** {% endhint %} **Example: Basic usage** {% code title="PYTHON" %} ```python from abc import ABC, abstractmethod, update_abstractmethods class AbstractParent(ABC): @abstractmethod def do_something(self): pass class ChildClass(AbstractParent): pass try: c = ChildClass() # ❌❌ except TypeError as e: print(e) def do_something_implementation(self): print("Doing something!") # Recompute abstract state ChildClass.do_something = do_something_implementation update_abstractmethods(ChildClass) c = ChildClass() # ✔️✔️ c.do_something() # Output: Doing something! ``` {% endcode %} ## 範例 – 計算面積 *** {% code title="PYTHON" %} ```python from abc import ABC, abstractmethod class Polygon(ABC): def __init__(self, sides): super().__init__() self.sides = sides @abstractmethod def area(self): """Verification of side length""" if not all(i > 0 for i in self.sides): raise ValueError("All side lengths must be positive") class Rectangle(Polygon): def __init__(self, sides): super().__init__(sides) def area(self): super().area() # Calculate rectangle area return self.sides[0] * self.sides[1] class Triangle(Polygon): def __init__(self, sides): super().__init__(sides) def area(self): super().area() # Calculate Heron's formula s = sum(self.sides) / 2 return (s * (s - self.sides[0]) * (s - self.sides[1]) * (s - self.sides[2])) ** 0.5 print(Rectangle([5, 10]).area())      # Output: 50 print(Triangle([20, 10, 15]).area())  # Output: 72.618 ``` {% endcode %} ### 範例 – 影像處理 *** {% code title="PYTHON" %} ```python from abc import ABC, abstractmethod from PIL import Image class ImageProcessor(ABC): def __init__(self, image_path): super().__init__() self.image = Image.open(image_path) @abstractmethod def process(self): if self.image.mode != 'RGB': raise ValueError("Image mode must be RGB") class ImageResizer(ImageProcessor): def __init__(self, image_path, size): super().__init__(image_path) self.size = size def process(self): super().process() # Resize the image return self.image.resize(self.size) class ImageRotator(ImageProcessor): def __init__(self, image_path, angle): super().__init__(image_path) self.angle = angle def process(self): super().process() # Rotate the image return self.image.rotate(self.angle) resizer = ImageResizer('image.jpg', (800, 800)) resized_image = resizer.process() resized_image.save('resized_image.jpg') rotator = ImageRotator('image.jpg', 90) rotated_image = rotator.process() rotated_image.save('rotated_image.jpg') ``` {% endcode %} ## 參考資料 *** [abc — Abstract Base Classes — Python 3.11.4 documentation](https://docs.python.org/3/library/abc.html) [PEP 3119 – 引入抽象基類 | peps.python.org](https://peps.python.org/pep-3119/) [Python 中的抽象基類 (abc) - GeeksforGeeks](https://www.geeksforgeeks.org/abstract-base-class-abc-in-python/) [Python interfaces: abandon ABC and switch to Protocols | by Oleg Sinavski | Level Up Coding](https://levelup.gitconnected.com/python-interfaces-choose-protocols-over-abc-3982e112342e) [python抽象類別 abc模組 - 知乎](https://zhuanlan.zhihu.com/p/508700685) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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