TODO


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- Need to complete, add custom wrapper function for those
  which could not be handled fully automatically
- Check the names generated, iD is bad, fix the name generation routine
- add examples, web page and python based test suite

Daniel Veillard

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# Authors:
#   Jason Gerard DeRose <jderose@redhat.com>
#
# Copyright (C) 2008  Red Hat
# see file 'COPYING' for use and warranty information
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

"""
Foundational classes and functions.
"""

import re
from constants import NAME_REGEX, NAME_ERROR
from constants import TYPE_ERROR, SET_ERROR, DEL_ERROR, OVERRIDE_ERROR


class ReadOnly(object):
    """
    Base class for classes that can be locked into a read-only state.

    Be forewarned that Python does not offer true read-only attributes for
    user-defined classes.  Do *not* rely upon the read-only-ness of this
    class for security purposes!

    The point of this class is not to make it impossible to set or to delete
    attributes after an instance is locked, but to make it impossible to do so
    *accidentally*.  Rather than constantly reminding our programmers of things
    like, for example, "Don't set any attributes on this ``FooBar`` instance
    because doing so wont be thread-safe", this class offers a real way to
    enforce read-only attribute usage.

    For example, before a `ReadOnly` instance is locked, you can set and delete
    its attributes as normal:

    >>> class Person(ReadOnly):
    ...     pass
    ...
    >>> p = Person()
    >>> p.name = 'John Doe'
    >>> p.phone = '123-456-7890'
    >>> del p.phone

    But after an instance is locked, you cannot set its attributes:

    >>> p.__islocked__()  # Is this instance locked?
    False
    >>> p.__lock__()  # This will lock the instance
    >>> p.__islocked__()
    True
    >>> p.department = 'Engineering'
    Traceback (most recent call last):
      ...
    AttributeError: locked: cannot set Person.department to 'Engineering'

    Nor can you deleted its attributes:

    >>> del p.name
    Traceback (most recent call last):
      ...
    AttributeError: locked: cannot delete Person.name

    However, as noted at the start, there are still obscure ways in which
    attributes can be set or deleted on a locked `ReadOnly` instance.  For
    example:

    >>> object.__setattr__(p, 'department', 'Engineering')
    >>> p.department
    'Engineering'
    >>> object.__delattr__(p, 'name')
    >>> hasattr(p, 'name')
    False

    But again, the point is that a programmer would never employ the above
    techniques *accidentally*.