in python tutorial added that python cannot hide its attributes from other classes. some thing such as private data in C++ or java..But also i know that we can use _ or __ to set some variables as privated  one but it is not enogh. I think it is a weak if it is not any thing to do it.
You are right that the _foo convention isn't sufficient to make data private; it's not supposed to be! Information hiding is not part of the design of Python. When writing programs in Python, you depend on the caller's good manners to leave your internals alone based on the naming convention and your documentation. Don't try to exert more control than this; we're all consenting adults.
There is a convention of naming internal-use methods like _foo with a single leading underscore; this serves more documentation purposes than anything else. Python name-mangles __foo attributes. Some people think this makes them more private, but it doesn't make them at all private, though it does make your classes harder to use, extend, and test. I never use them.
information hiding in python