Pop Quiz #8.2 (Private Method/Variable)

15.9. PRIVATE VARIABLES AND PRIVATE METHODS

• Most languages that define private variables do so through the use of the keyword “private” or something similar. 
• The convention in Python is simpler, and it also makes it easier to immediately see what is private and what isn’t. 
•  Any method or instance variable whose name begins—but doesn’t end—with a double underscore (__) is private;
  • anything else isn’t private.
  • class A:
    • __x = 1     # private
    • __y__ = 2 # not private
    • _z =3        # not private
• The mechanism used to provide privacy "mangles" the name of private variables and private methods when the code is compiled to bytecode.
  • What specifically happens is that _classname is prepended to the variable name:
• The purpose is to prevent any accidental accesses.
  • If someone wanted to, he could deliberately simulate the mangling and access the value.
  • But performing the mangling in this easily readable form makes debugging easy.
• Private methods/variables cannot be created outside the class definition.