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#
# descriptors.py: classes implementing pythons "descriptor" protocol,
# which are usable as python properties
#
# Peter Jones <pjones@redhat.com>
#
# Copyright 2005 Red Hat, Inc.
#
# This software may be freely redistributed under the terms of the GNU
# library public license.
#
# You should have received a copy of the GNU Library Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
#
class SimpleBoolDescriptor(object):
"""A data descriptor which constrains its values to True and False."""
def __init__(self):
self.val = False
def __get__(self, obj, objtype):
return self.val
def __set__(self, obj, val):
if not isinstance(val, type(True)):
raise TypeError, "value is not True of False"
self.val = val
class BoolDescriptor(SimpleBoolDescriptor):
"""A data descriptor which constrains its values to True
and False, and may be set immutable
"""
immutable = SimpleBoolDescriptor()
def __set__(self, obj, val):
if self.immutable:
raise RuntimeError, "attribute is immutable"
SimpleBoolDescriptor.__set__(self, obj, val)
class TristateDescriptor(BoolDescriptor):
"""A data descriptor which constrains its values to True,
False, and None, and which may be set immutable
"""
immutable = SimpleBoolDescriptor()
def __set__(self, obj, val):
if self.immutable:
raise RuntimeError, "attribute is immutable"
if isinstance(val, type(None)):
self.val = None
return
BoolDescriptor.__set__(self, obj, val)
class NonNegativeIntegerDescriptor(object):
"""A data descriptor which constrains its values to non-negative integers
"""
immutable = SimpleBoolDescriptor()
def __set__(self, obj, val):
if self.immutable:
raise RuntimeError, "attribute is immutable"
if not isinstance(val, type(int(1))) and \
not isinstance(val, type(long(1))):
raise TypeError, type(val)
if val < 0:
raise ValueError, "%s is less than 0" % (int(val,))
self.val = val
def __get__(self, obj, objtype):
return self.val
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