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# vim: set fileencoding=utf-8 :
#
# (C) 2011 Guido Guenther <agx@sigxcpu.org>
# 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 2 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, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
"""
A switch with three states: on|off|auto
"""
class Tristate(object):
"""Tri-state value: on, off or auto """
ON = True # state is on == do it
OFF = False # state is off == don't do it
AUTO = -1 # autodetect == do if possible
# We accept true as alias for on and false as alias for off
_VALID_NAMES = [ 'on', 'off', 'true', 'false', 'auto' ]
def __init__(self, val):
if type(val) in [ type(t) for t in (True, 1) ]:
if val > 0:
self._state = self.ON
elif val < 0:
self._state = self.AUTO
else:
self._state = self.OFF
elif type(val) in [ type(t) for t in ("", "") ]:
if val.lower() in [ 'on', 'true' ]:
self._state = self.ON
elif val.lower() in [ 'auto' ]:
self._state = self.AUTO
else:
self._state = self.OFF
elif type(val) is Tristate:
self._state = val.state
else:
raise TypeError
def __repr__(self):
"""
>>> Tristate('on').__repr__()
'on'
>>> Tristate(True).__repr__()
'on'
>>> Tristate(False).__repr__()
'off'
>>> Tristate('auto').__repr__()
'auto'
"""
if self._state == self.ON:
return 'on'
elif self._state == self.AUTO:
return 'auto'
else:
return 'off'
def __bool__(self):
"""
>>> Tristate('on').__nonzero__()
True
>>> Tristate('auto').__nonzero__()
True
>>> Tristate('off').__nonzero__()
False
"""
return self._state is not self.OFF
@property
def state(self):
"""Get current state"""
return self._state
def is_auto(self):
return [False, True][self._state == self.AUTO]
def is_on(self):
return [False, True][self._state == self.ON]
def is_off(self):
return [False, True][self._state == self.OFF]
def do(self, function, *args, **kwargs):
"""
Run function if tristate is on or auto, only report a failure if
tristate is on since failing is o.k. for autodetect.
"""
if self.is_off():
return True
success = function(*args, **kwargs)
if not success:
return [True, False][self.is_on()]
return True
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