Python Pocket Reference, 3rd Edition

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Python Pocket Reference

Pseudo-Private Attributes

By default, all attribute names in modules and classes are vis-

ible everywhere. Special conventions allow some limited

data-hiding, but are mostly designed to prevent name colli-

sions (see also the section “Name conventions,” earlier in

this book).

Module privates

Names in modules with a single underscore (e.g., _X), and

those not listed on the module’s

__all__ list, are not copied

over when a client uses

from module import *. This is not

strict privacy, though, as such names can still be accessed

apart from the

from..* statement.

Class privates

Names anywhere within class statements with two leading

underscores only (e.g.,

__X) are mangled at compile time to

include the enclosing class name as a prefix (e.g.,

_Class__X).

The added class-name prefix localizes such names to the

enclosing class and thus makes them distinct in both the

self

instance object and the class hierarchy.

This helps to avoid clashes that arise in the single instance

object at the bottom of the inheritance chain (all assign-

ments to

self.attr anywhere in a framework change the sin-

gle instance namespace). This is not strict privacy, though, as

such attributes can still be accessed via the mangled name.

New Style Classes

In Version 2.2 and later, inheritance search order can be

slightly different in multiple inheritance diamonds if a super-

class inherits from

object (e.g., class A(object) ...