PyCharm and debugging private attributes

Question

I use PyCharm Community Edition 3.4.

I have added self.__a to Watches.

This is my example:

class Box:
    def __init__(self, a, b, c):
        self.__a = a
        self._b  = b
        self.c   = c
        d = 0 #Breakpoint.


a = Box(1, 2, 3)

So, I start debugging and stop at the breakpoint. The self.__a watch shows {AttributeError}'Box' object has no attribute 'a'.

I press Alt + F8 and evaluate self.__a = a. The result is None.

Then I evaluate self.__a and the result is 1.

My watch for self.__a still shows {AttributeError}'Box' object has no attribute 'a'. I delete it. Then I add another watch self.__a. It shows 1.

Could you clarify what is going on here?

Answer 1

it is because box has no __a

it gets name mangled ...

see also: Name_mangling#Python

it becomes

Box._Box__a

and if you change it to watch

self._Box__a 

it will show you the proper value

but it should also show up in the variables list view (in the center of the debug run panel)