|An Introduction to Python|
by Guido van Rossum and Fred L. Drake, Jr.
Paperback (6"x9"), 124 pages
RRP £12.95 ($19.95)
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9.6 Private Variables
There is limited support for class-private
identifiers. Any identifier of the form
__spam (at least two
leading underscores, at most one trailing underscore) is textually
classname is the
current class name with leading underscore(s) stripped. This mangling
is done without regard to the syntactic position of the identifier, so
it can be used to define class-private instance and class variables,
methods, variables stored in globals, and even variables stored in instances.
private to this class on instances of other classes. Truncation
may occur when the mangled name would be longer than 255 characters.
Outside classes, or when the class name consists of only underscores,
no mangling occurs.
Name mangling is intended to give classes an easy way to define "private" instance variables and methods, without having to worry about instance variables defined by derived classes, or mucking with instance variables by code outside the class. Note that the mangling rules are designed mostly to avoid accidents; it still is possible for a determined soul to access or modify a variable that is considered private. This can even be useful in special circumstances, such as in the debugger, and that's one reason why this loophole is not closed. (Buglet: derivation of a class with the same name as the base class makes use of private variables of the base class possible.)
Notice that code passed to
execfile() does not consider the classname of the invoking
class to be the current class; this is similar to the effect of the
global statement, the effect of which is likewise restricted to
code that is byte-compiled together. The same restriction applies to
delattr(), as well as
|ISBN 0954161769||An Introduction to Python||See the print edition|