Inheritance private attributes

[vaison]

Hello guys,

I'm trying to inherit private attributes (self.__attrib), but when I use the parent __init__ method this private attributes doesn't inherit. For example:

class Primary():
	def __init__(self, param1, param2):
		self.param1 = param1
		self.__param2 = param2

	def getP1(self):
		return self.param1

	def getP2(self):
		return self.__param2

class Secondary(Primary):
	def __init__(self, param1, param2, param3):
		Primary.__init__(self, param1, param2)
		self.__param3 = param3

	def getP3(self):
		return self.__param3

	def test(self):
		print (self.__param2)

#Main

p = Primary('a', 'b')
s = Secondary('a', 'b', 'c')

s.test()

When I try to access self.__param2 in Secondary instance, there is an error:

Error:
Traceback (most recent call last):
  File "class_test.py", line 38, in <module>
    s.test()
  File "class_test.py", line 21, in test
    print (self.__param2)
AttributeError: 'Secondary' object has no attribute '_Secondary__param2'

I think in three solutions:
1 - Use public attributes: self.param2 instead of self.__param2. It is not an important problem, but conceptually, the attributes that will not be accessed out of class, must be private. Not?

2- Not reutilize the Primary __init__ constructor. But we are wasting inheritance potencial, not? Like this:

class Secondary(Primary):
	def __init__(self, param1, param2, param3):
		self.param1 = param1
		self.__param2 = param2
		self.__param3 = param3

3- Use parent get() method when I need it (maybe the best solution):

def test(self):
		print (Primary.getP2(self))

Any best solution? Maybe the best is the third option, not?

Thanks a lot