~bzr-pqm/bzr/bzr.dev

# 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)

# 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 = {}