Explanation and Examples of Python Special Methods (__unicode__, __delattr__, __del__, __dict__, __all__)

In Python, several special methods allow developers to customize object behavior, such as __unicode__, __delattr__, __del__, __dict__, and __all__.

__unicode__() is used in Python 2 to define an object's Unicode string representation, invoked by the unicode() function or print statements.

__delattr__() is called when the del statement removes an attribute, enabling custom deletion logic.

__del__() is executed when an object is garbage‑collected, allowing cleanup of resources.

__dict__() provides a dictionary of an object's attributes, accessible via obj.__dict__ or vars(obj).

__all__ defines the public symbols of a module; when using from module import *, only names listed in __all__ are imported.

Example code demonstrates each method:

class MyClass:
    def __init__(self, value):
        self.value = value
    def __unicode__(self):
        return u"MyClass with value: %s" % self.value

obj = MyClass(42)
print(unicode(obj))  # Output: MyClass with value: 42

class MyClass:
    def __init__(self, value):
        self.value = value
    def __delattr__(self, name):
        if name == 'value':
            raise AttributeError("Cannot delete attribute 'value'")

obj = MyClass(42)
del obj.value  # Raises AttributeError: Cannot delete attribute 'value'

class MyClass:
    def __del__(self):
        print("MyClass object is being destroyed")

obj = MyClass()
del obj  # Output: MyClass object is being destroyed

class MyClass:
    def __init__(self, value):
        self.value = value
obj = MyClass(42)
print(obj.__dict__)  # Output: {'value': 42}

# my_module.py
__all__ = ['my_function']
def my_function():
    return "Hello, world!"
def internal_function():
    return "This function is not part of __all__"

# In another file
from my_module import *
print(my_function())  # Output: Hello, world!
print(internal_function())  # Raises NameError

Note that __unicode__() is only relevant for Python 2; in Python 3 the __str__() method should be used, and __all__ applies to modules rather than regular classes.