Ben Finney wrote: > Alex Martelli <[EMAIL PROTECTED]> wrote: >>Ben Finney <[EMAIL PROTECTED]> wrote: >> >>>How can a (user-defined) class ensure that its instances are >>>immutable, like an int or a tuple, without inheriting from those >>>types? >> >>You can make a good start by defining __setattr__, __delattr__ (and >>__setitem__ and __delitem__ if your class is a container) to raise >>exceptions. >>Remember that your redefined __setattr__ IS "in place" even when >>you're initializing your istance, so remember to delegate attribute >>setting to the superclass (the other special methods mentioned above >>are less likely to byte you). > > So, for a class that needs to set attributes in __init__ (but after > that, become immutable), how do I get around this? Should I make a > _FooFunctionality class, and then inherit from that to make Foo as the > immutable class that actually gets exported?
Typically, constants are set up in __new__ (which happens before __init__), because by __init__ time the object is built. Remember not to complain that you have no copy operation, because there is no such thing as a copy of a constant (the original constant is good enough). --Scott David Daniels [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
