Can't use class variable with private nested class

[tron.thomas@verizon.net]

The following code will print a message only once:
class PrintOnce:
printOnce = True

def __init__(self):
if PrintOnce.print Once:
print 'Printing once.'
PrintOnce.print Once = False

first = PrintOnce()
second = PrintOnce()

The following code will do the same thing for a nested class:
class Outer:
class Inner:
printOnce = True

def __init__(self):
if Outer.Inner.pri ntOnce:
print 'Printing once.'
Outer.Inner.pri ntOnce = False

def __init__(self):
first = Outer.Inner()
second = Outer.Inner()

outer = Outer()


However the following code, which has a private nested class, does not
work:
class Public:
class __Private:
printOnce = True

def __init__(self):
print 'Creating a __Private instance'
if Public.__Privat e.printOnce:
print 'Printing once.'
Public.__Privat e.printOnce = False

def __init__(self):
print 'Creating a Public instance'
first = Public.__Privat e()
second = Public.__Privat e()

public = Public()

Attempting to run the code will produce this error:
AttributeError: class Public has no attribute '_Private__Priv ate'

What can be done so that this private nested class can have the same
functionality as the public nested class?

[Alex Martelli]

Re: Can't use class variable with private nested class

<tron.thomas@ve rizon.netwrote:
...

class Outer:
class Inner:
printOnce = True
>
def __init__(self):
if Outer.Inner.pri ntOnce:
print 'Printing once.'
Outer.Inner.pri ntOnce = False
>
def __init__(self):
first = Outer.Inner()
second = Outer.Inner()
>
outer = Outer()
>
>
However the following code, which has a private nested class, does not
work:
class Public:
class __Private:
printOnce = True
>
def __init__(self):
print 'Creating a __Private instance'
if Public.__Privat e.printOnce:

When, anywhere "immediatel y inside" a class named X, you use a name
__foo starting with two underscores, that name is mangled to _X__foo.
Here, you're inside class __Private, so the mangling of __Private is to
_Private__Priva te (I'd actually have expected more stray underscores
hither and thither, but that's the gist of it).

print 'Printing once.'
Public.__Privat e.printOnce = False
>
def __init__(self):
print 'Creating a Public instance'
first = Public.__Privat e()
second = Public.__Privat e()
>
public = Public()
>
Attempting to run the code will produce this error:
AttributeError: class Public has no attribute '_Private__Priv ate'
>
What can be done so that this private nested class can have the same
functionality as the public nested class?

Forget all the naming silliness and use self.__class__. printOnce
instead.


Alex

[tron.thomas@verizon.net]

Re: Can't use class variable with private nested class

On Mar 27, 10:08 pm, a...@mac.com (Alex Martelli) wrote:

>
Forget all the naming silliness and use self.__class__. printOnce
instead.
>
Alex

I tried self.__class__. printOnce and that worked. Thanks for your
help.