class Secret: def __init__(self): self.public = "Everyone sees this" self._protected = "Please don't touch" self.__private = "Name mangled" Simatic S7 F Systems V6.4 Download
o = Optimized(1, 2) o.z = 3 # Raises AttributeError! Cannot add new attributes. You save memory but lose the ability to dynamically add attributes. Part 3: Descriptors Descriptors are the secret sauce behind properties, methods, and class methods. A descriptor is an object that defines one of __get__ , __set__ , or __delete__ . Kemonokko Tsuushin The Animation 01 Audio La Full
print([cls.__name__ for cls in D.mro()]) # Output: ['D', 'B', 'C', 'A', 'object'] Python searches depth-first, then left-to-right, ensuring no class is visited before its parents are. Understanding MRO is critical for debugging complex inheritance hierarchies. Python does not have private , protected , or public keywords like Java/C++. Instead, it relies on convention and name mangling. 1. Public (Default) Everything is accessible. 2. Protected ( _variable ) A single underscore is a convention. It tells other developers: "This is an internal implementation detail; do not access it directly." Python does not enforce this; it is purely social. 3. Private ( __variable ) A double underscore triggers Name Mangling . Python changes the name of the variable to _ClassName__variable at compile time. This prevents accidental name collisions in subclasses, but it does not truly prevent access if someone tries hard enough.
obj = MyClass() obj.greet() # Hello A metaclass allows you to intercept the creation of a class, inspect its attributes, or modify its structure before the class is fully defined. You use a metaclass by inheriting from type .
class Optimized: __slots__ = ['x', 'y'] # Fixed attribute set
p = Person() p.name = "Alice" # Works # p.name = 123 # Raises TypeError This is how Django models and SQLAlchemy columns work under the hood. In Python, classes are objects too. Just as instances are created by classes, classes are created by metaclasses. The default metaclass is type . type(name, bases, dict) You can dynamically create a class using the type function:
a = [1, 2] b = [1, 2]
def __set__(self, obj, value): if not isinstance(value, str): raise TypeError(f"{self.name} must be a string") obj.__dict__[self.name] = value