How are private variables and methods declared inside a class in Python?

In Python, there are no true private variables and methods like in some other languages, but there are conventions and mechanisms to indicate their privacy.

1. A single underscore _var is a convention that the variable or method is intended for internal use (unofficial privacy).

2. Double underscore __var leads to name mangling, meaning the variable's name inside the class is changed to make external access more difficult.

Example:

class MyClass:
    def __init__(self):
        self._internal_var = 1  # conditionally private
        self.__private_var = 2  # name will be changed

    def __private_method(self):
        print("This is a private method")

obj = MyClass()
print(obj._internal_var)       # accessible, but not recommended
# print(obj.__private_var)    # will cause an error
print(obj._MyClass__private_var)  # access via name mangling

Thus, double underscores help hide variables and methods from direct access, but they are not fully private.