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FWIW that section used to be called "Private variables through name mangling" back in 1.5, and started by saying "There is now limited support for class-private identifiers.".
PEP8 [0] also talks about the name mangling in several places, and carefully avoids the use of "private":
 """
 To avoid name clashes with subclasses, use two leading underscores to
 invoke Python's name mangling rules.
 Python mangles these names with the class name: if class Foo has an
 attribute named __a, it cannot be accessed by Foo.__a. (An insistent
 user could still gain access by calling Foo._Foo__a.) Generally, double
 leading underscores should be used only to avoid name conflicts with
 attributes in classes designed to be subclassed.
 """
And it even includes the following two notes:
 """
 We don't use the term "private" here, since no attribute is really
 private in Python (without a generally unnecessary amount of work).
 """
 """
 Not everyone likes name mangling. Try to balance the
 need to avoid accidental name clashes with potential use by
 advanced callers.
 """
[0]: http://www.python.org/dev/peps/pep-0008/