PYTHON

private instance attribute python

# Square Class: Define a Square with private instance
class Square:
	def __init__(self, size=0):
      # initialise variables
      self.__size = size

how to declare private attribute in python

class Base:
	def __init__(self):
    	self.__private_attribute = 2 #two underscores before attribute declare it as private

private attributes python

# Making attributes private
# Naming convention, when want to make attribute private, precede it with two underscores __
# e.g. self.__private_data. Then Python automatically renames it as _ClassName__private_date (name mangling)
# so instance.__private_data will not access this attribute
# but instance._PrivateClass__private_data will still be able to access it. 

class PrivateClass:
    """Class with public and private attributes."""

    def __init__(self):
        """Initialize the public and private attributes."""
        self.public_data = "public"  # public attribute
        self.__private_data = "private"  # private attribute
        

instance = PrivateClass()
instance.public_data
# 'public'

instance.__private_data
# AttributeError: 'PrivateClass' object has no attribute '__private_data'

instance._PrivateClass__private_data
# 'private'

instance._PrivateClass__private_data = 'modified'
instance._PrivateClass__private_data
# 'modified'