What is the difference between the parameters _value and __value in Python?

In Python, _value and __value are naming conventions, not strict visibility rules.

• _value (single underscore): Indicates that the variable or method is "internal" or "protected". It is a convention that they should not be accessed directly outside the class or module.

• __value (double underscore): Triggers name mangling. Python automatically changes the name of the variable or method to _ClassName__value to avoid conflicts in inheritance hierarchies. It does not make the variable fully private, but makes accidental access more difficult and helps avoid name clashes.

Summary: _value — convention for "protected" members; __value — name mangling to prevent name conflicts in inheritance.

class MyClass:
    def __init__(self):
        self._protected_value = 10   # Protected by convention
        self.__private_value = 20   # Name mangled

obj = MyClass()
print(obj._protected_value) # Accessible but discouraged
# print(obj.__private_value) # AttributeError
print(obj._MyClass__private_value) # Access via mangled name