[Tutor] Public, private and protected member variables.

[Marc Barry]

Dear All:

I have a question regarding the existence of protected members in Python. 
Basically, in a language like Java we have public, private and protected 
member variables. But in Python I only know of public and private. I would 
like to inherit from a class and be able to modify parent member variables, 
but I would not like any class that doesn't inherit from the parent to be 
able to modify the member variables (i.e. Protected concept in Java).

Here is a simple example:

#------------------------------------------------------------
class Car:
	def __init__(self, colour):
		self.__colour = colour


class Ferrari(Car):
	def __init__(self, model, colour):

		Car.__init__(self, colour)
		self.__model = model

	def printColour(self):
		print self.__colour

a_ferrari = Ferrari("Enzo", "Red")
print dir(a_ferrari)
a_ferrari.printColour()
#------------------------------------------------------------

The output from running this script is:

['_Car__colour', '_Ferrari__model', '__doc__', '__init__', '__module__', 
'printColour']
Traceback (most recent call last):
  File "inheritance.py", line 19, in ?
    a_ferrari.printColour()
  File "inheritance.py", line 15, in printColour
    self.__colour
AttributeError: Ferrari instance has no attribute '_Ferrari__colour'

As you can see the __colour member variable of Car is not visible in the 
Ferrari class since it appears that appending '__' on a variable makes it 
private and not protected. Is there a way to make a variable protected in 
Python?

If I expose a variable in Car as public ,then I will allow users of the 
class to modify it directly. I would like to avoid this since that fixes my 
implementation to being always having to provide a variable named "colour" 
for example. Also, this is just a simplification of my problem as my class 
is much more complicated with a lot of gettable and settable properties in 
the parent object (Which I want to inherit).

Regards,

Marc Barry
marc_barry at hotmail.com

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