122 lines
3.5 KiB
Python
122 lines
3.5 KiB
Python
#!/usr/bin/env python3
|
|
#
|
|
# Copyright (c) 2019, The OpenThread Authors.
|
|
# All rights reserved.
|
|
#
|
|
# Redistribution and use in source and binary forms, with or without
|
|
# modification, are permitted provided that the following conditions are met:
|
|
# 1. Redistributions of source code must retain the above copyright
|
|
# notice, this list of conditions and the following disclaimer.
|
|
# 2. Redistributions in binary form must reproduce the above copyright
|
|
# notice, this list of conditions and the following disclaimer in the
|
|
# documentation and/or other materials provided with the distribution.
|
|
# 3. Neither the name of the copyright holder nor the
|
|
# names of its contributors may be used to endorse or promote products
|
|
# derived from this software without specific prior written permission.
|
|
#
|
|
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
|
|
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
|
|
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
|
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
|
|
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
|
|
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
|
|
# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
|
|
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
|
|
# POSSIBILITY OF SUCH DAMAGE.
|
|
#
|
|
|
|
nullField = None
|
|
|
|
|
|
class NullField(object):
|
|
"""
|
|
Represents a null field that does not exists.
|
|
"""
|
|
|
|
def __new__(cls, *args, **kwargs):
|
|
global nullField
|
|
|
|
if nullField is None:
|
|
nullField = object.__new__(cls, *args, **kwargs)
|
|
|
|
return nullField
|
|
|
|
def __init__(self):
|
|
assert self is nullField
|
|
|
|
def __bool__(self):
|
|
"""
|
|
NullField is always treated as False.
|
|
"""
|
|
return False
|
|
|
|
def __getattr__(self, item):
|
|
"""
|
|
Any sub field of the NullField is NullField itself.
|
|
"""
|
|
return self
|
|
|
|
def __setattr__(self, key, value):
|
|
pass
|
|
|
|
def __len__(self) -> 0:
|
|
return 0
|
|
|
|
def __eq__(self, other):
|
|
"""
|
|
NullField is always not equal to any other value.
|
|
"""
|
|
return False
|
|
|
|
def __ne__(self, other):
|
|
return True
|
|
|
|
def __lt__(self, other):
|
|
"""
|
|
Comparing NullField to any other value gets False.
|
|
"""
|
|
return False
|
|
|
|
def __le__(self, other):
|
|
"""
|
|
Comparing NullField to any other value gets False.
|
|
"""
|
|
return False
|
|
|
|
def __gt__(self, other):
|
|
"""
|
|
Comparing NullField to any other value gets False.
|
|
"""
|
|
return False
|
|
|
|
def __ge__(self, other):
|
|
"""
|
|
Comparing NullField to any other value gets False.
|
|
"""
|
|
return False
|
|
|
|
def __str__(self):
|
|
return "nullField"
|
|
|
|
def __repr__(self):
|
|
return 'nullField'
|
|
|
|
|
|
NullField()
|
|
|
|
if __name__ == '__main__':
|
|
assert nullField is NullField()
|
|
assert not nullField, repr(nullField)
|
|
assert nullField != nullField, repr(nullField)
|
|
assert nullField != 0
|
|
assert not (nullField > 1)
|
|
assert not (nullField < 1)
|
|
assert not (nullField < nullField)
|
|
assert not (nullField > nullField)
|
|
assert bool(nullField) is False
|
|
assert nullField != ""
|
|
assert nullField != None # noqa
|
|
assert nullField is not None
|