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# Copyright (C) 2009 Canonical Ltd
#
# 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
"""The pure-python implementation of the StaticTuple type.
Note that it is generally just implemented as using tuples of tuples of
strings.
"""
class StaticTuple(tuple):
"""A static type, similar to a tuple of strings."""
def __new__(cls, *args):
# Make the empty StaticTuple a singleton
if not args and _empty_tuple is not None:
return _empty_tuple
return tuple.__new__(cls, args)
def __init__(self, *args):
"""Create a new 'StaticTuple'"""
for bit in args:
if type(bit) not in (str, StaticTuple):
raise TypeError('key bits must be strings or StaticTuple')
num_keys = len(args)
if num_keys < 0 or num_keys > 255:
raise ValueError('must have 1 => 256 key bits')
# We don't need to pass args to tuple.__init__, because that was
# already handled in __new__.
tuple.__init__(self)
def __repr__(self):
return '%s%s' % (self.__class__.__name__, tuple.__repr__(self))
def as_tuple(self):
return self
def intern(self):
return _interned_tuples.setdefault(self, self)
@staticmethod
def from_sequence(seq):
"""Convert a sequence object into a StaticTuple instance."""
if isinstance(seq, StaticTuple):
# it already is
return seq
return StaticTuple(*seq)
# Have to set it to None first, so that __new__ can determine whether
# the _empty_tuple singleton has been created yet or not.
_empty_tuple = None
_empty_tuple = StaticTuple()
_interned_tuples = {}
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