~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2010, 2011 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

"""ControlDir is the basic control directory class.

The ControlDir class is the base for the control directory used

by all bzr and foreign formats. For the ".bzr" implementation,

see bzrlib.bzrdir.BzrDir.

"""

from bzrlib.lazy_import import lazy_import

lazy_import(globals(), """

import textwrap

from bzrlib import (

    cleanup,

    errors,

    graph,

    revision as _mod_revision,

    urlutils,

    )

from bzrlib.push import (

    PushResult,

    )

from bzrlib.trace import (

    mutter,

    )

from bzrlib.transport import (

    get_transport,

    local,

    )

""")

from bzrlib import registry

class ControlComponent(object):

    """Abstract base class for control directory components.

    This provides interfaces that are common across controldirs,

    repositories, branches, and workingtree control directories.

    They all expose two urls and transports: the *user* URL is the

    one that stops above the control directory (eg .bzr) and that

    should normally be used in messages, and the *control* URL is

    under that in eg .bzr/checkout and is used to read the control

    files.

    This can be used as a mixin and is intended to fit with

    foreign formats.

    """

    @property

    def control_transport(self):

        raise NotImplementedError

    @property

    def control_url(self):

        return self.control_transport.base

    @property

    def user_transport(self):

        raise NotImplementedError

    @property

    def user_url(self):

        return self.user_transport.base

class ControlDir(ControlComponent):

    """A control directory.

    While this represents a generic control directory, there are a few

    features that are present in this interface that are currently only

    supported by one of its implementations, BzrDir.

    These features (bound branches, stacked branches) are currently only

    supported by Bazaar, but could be supported by other version control

    systems as well. Implementations are required to raise the appropriate

    exceptions when an operation is requested that is not supported.

    This also makes life easier for API users who can rely on the

    implementation always allowing a particular feature to be requested but

    raising an exception when it is not supported, rather than requiring the

    API users to check for magic attributes to see what features are supported.

    """

    def can_convert_format(self):

        """Return true if this controldir is one whose format we can convert

        from."""

        return True

    def list_branches(self):

        """Return a sequence of all branches local to this control directory.

        """

        try:

            return [self.open_branch()]

        except (errors.NotBranchError, errors.NoRepositoryPresent):

            return []

    def is_control_filename(self, filename):

        """True if filename is the name of a path which is reserved for

        controldirs.

        :param filename: A filename within the root transport of this

            controldir.

        This is true IF and ONLY IF the filename is part of the namespace reserved

        for bzr control dirs. Currently this is the '.bzr' directory in the root

        of the root_transport. it is expected that plugins will need to extend

        this in the future - for instance to make bzr talk with svn working

        trees.

        """

        raise NotImplementedError(self.is_control_filename)

    def needs_format_conversion(self, format=None):

        """Return true if this controldir needs convert_format run on it.

        For instance, if the repository format is out of date but the

        branch and working tree are not, this should return True.

        :param format: Optional parameter indicating a specific desired

                       format we plan to arrive at.

        """

        raise NotImplementedError(self.needs_format_conversion)

    def destroy_repository(self):

        """Destroy the repository in this ControlDir."""

        raise NotImplementedError(self.destroy_repository)

    def create_branch(self, name=None, repository=None):

        """Create a branch in this ControlDir.

        :param name: Name of the colocated branch to create, None for

            the default branch.

        The controldirs format will control what branch format is created.

        For more control see BranchFormatXX.create(a_controldir).

        """

        raise NotImplementedError(self.create_branch)

    def destroy_branch(self, name=None):

        """Destroy a branch in this ControlDir.

        :param name: Name of the branch to destroy, None for the default 

            branch.

        """

        raise NotImplementedError(self.destroy_branch)

    def create_workingtree(self, revision_id=None, from_branch=None,

        accelerator_tree=None, hardlink=False):

        """Create a working tree at this ControlDir.

        :param revision_id: create it as of this revision id.

        :param from_branch: override controldir branch 

            (for lightweight checkouts)

        :param accelerator_tree: A tree which can be used for retrieving file

            contents more quickly than the revision tree, i.e. a workingtree.

            The revision tree will be used for cases where accelerator_tree's

            content is different.

        """

        raise NotImplementedError(self.create_workingtree)

    def destroy_workingtree(self):

        """Destroy the working tree at this ControlDir.

        Formats that do not support this may raise UnsupportedOperation.

        """

        raise NotImplementedError(self.destroy_workingtree)

    def destroy_workingtree_metadata(self):

        """Destroy the control files for the working tree at this ControlDir.

        The contents of working tree files are not affected.

        Formats that do not support this may raise UnsupportedOperation.

        """

        raise NotImplementedError(self.destroy_workingtree_metadata)

    def get_branch_reference(self, name=None):

        """Return the referenced URL for the branch in this controldir.

        :param name: Optional colocated branch name

        :raises NotBranchError: If there is no Branch.

        :raises NoColocatedBranchSupport: If a branch name was specified

            but colocated branches are not supported.

        :return: The URL the branch in this controldir references if it is a

            reference branch, or None for regular branches.

        """

        if name is not None:

            raise errors.NoColocatedBranchSupport(self)

        return None

    def get_branch_transport(self, branch_format, name=None):

        """Get the transport for use by branch format in this ControlDir.

        Note that bzr dirs that do not support format strings will raise

        IncompatibleFormat if the branch format they are given has

        a format string, and vice versa.

        If branch_format is None, the transport is returned with no

        checking. If it is not None, then the returned transport is

        guaranteed to point to an existing directory ready for use.

        """

        raise NotImplementedError(self.get_branch_transport)

    def get_repository_transport(self, repository_format):

        """Get the transport for use by repository format in this ControlDir.

        Note that bzr dirs that do not support format strings will raise

        IncompatibleFormat if the repository format they are given has

        a format string, and vice versa.

        If repository_format is None, the transport is returned with no

        checking. If it is not None, then the returned transport is

        guaranteed to point to an existing directory ready for use.

        """

        raise NotImplementedError(self.get_repository_transport)

    def get_workingtree_transport(self, tree_format):

        """Get the transport for use by workingtree format in this ControlDir.

        Note that bzr dirs that do not support format strings will raise

        IncompatibleFormat if the workingtree format they are given has a

        format string, and vice versa.

        If workingtree_format is None, the transport is returned with no

        checking. If it is not None, then the returned transport is

        guaranteed to point to an existing directory ready for use.

        """

        raise NotImplementedError(self.get_workingtree_transport)

    def open_branch(self, name=None, unsupported=False,

                    ignore_fallbacks=False):

        """Open the branch object at this ControlDir if one is present.

        If unsupported is True, then no longer supported branch formats can

        still be opened.

        TODO: static convenience version of this?

        """

        raise NotImplementedError(self.open_branch)

    def open_repository(self, _unsupported=False):

        """Open the repository object at this ControlDir if one is present.

        This will not follow the Branch object pointer - it's strictly a direct

        open facility. Most client code should use open_branch().repository to

        get at a repository.

        :param _unsupported: a private parameter, not part of the api.

        TODO: static convenience version of this?

        """

        raise NotImplementedError(self.open_repository)

    def find_repository(self):

        """Find the repository that should be used.

        This does not require a branch as we use it to find the repo for

        new branches as well as to hook existing branches up to their

        repository.

        """

        raise NotImplementedError(self.find_repository)

    def open_workingtree(self, _unsupported=False,

                         recommend_upgrade=True, from_branch=None):

        """Open the workingtree object at this ControlDir if one is present.

        :param recommend_upgrade: Optional keyword parameter, when True (the

            default), emit through the ui module a recommendation that the user

            upgrade the working tree when the workingtree being opened is old

            (but still fully supported).

        :param from_branch: override controldir branch (for lightweight

            checkouts)

        """

        raise NotImplementedError(self.open_workingtree)

    def has_branch(self, name=None):

        """Tell if this controldir contains a branch.

        Note: if you're going to open the branch, you should just go ahead

        and try, and not ask permission first.  (This method just opens the

        branch and discards it, and that's somewhat expensive.)

        """

        try:

            self.open_branch(name)

            return True

        except errors.NotBranchError:

            return False

    def has_workingtree(self):

        """Tell if this controldir contains a working tree.

        This will still raise an exception if the controldir has a workingtree

        that is remote & inaccessible.

        Note: if you're going to open the working tree, you should just go ahead

        and try, and not ask permission first.  (This method just opens the

        workingtree and discards it, and that's somewhat expensive.)

        """

        try:

            self.open_workingtree(recommend_upgrade=False)

            return True

        except errors.NoWorkingTree:

            return False

    def cloning_metadir(self, require_stacking=False):

        """Produce a metadir suitable for cloning or sprouting with.

        These operations may produce workingtrees (yes, even though they're

        "cloning" something that doesn't have a tree), so a viable workingtree

        format must be selected.

        :require_stacking: If True, non-stackable formats will be upgraded

            to similar stackable formats.

        :returns: a ControlDirFormat with all component formats either set

            appropriately or set to None if that component should not be

            created.

        """

        raise NotImplementedError(self.cloning_metadir)

    def checkout_metadir(self):

        """Produce a metadir suitable for checkouts of this controldir."""

        return self.cloning_metadir()

    def sprout(self, url, revision_id=None, force_new_repo=False,

               recurse='down', possible_transports=None,

               accelerator_tree=None, hardlink=False, stacked=False,

               source_branch=None, create_tree_if_local=True):

        """Create a copy of this controldir prepared for use as a new line of

        development.

        If url's last component does not exist, it will be created.

        Attributes related to the identity of the source branch like

        branch nickname will be cleaned, a working tree is created

        whether one existed before or not; and a local branch is always

        created.

        if revision_id is not None, then the clone operation may tune

            itself to download less data.

        :param accelerator_tree: A tree which can be used for retrieving file

            contents more quickly than the revision tree, i.e. a workingtree.

            The revision tree will be used for cases where accelerator_tree's

            content is different.

        :param hardlink: If true, hard-link files from accelerator_tree,

            where possible.

        :param stacked: If true, create a stacked branch referring to the

            location of this control directory.

        :param create_tree_if_local: If true, a working-tree will be created

            when working locally.

        """

        operation = cleanup.OperationWithCleanups(self._sprout)

        return operation.run(url, revision_id=revision_id,

            force_new_repo=force_new_repo, recurse=recurse,

            possible_transports=possible_transports,

            accelerator_tree=accelerator_tree, hardlink=hardlink,

            stacked=stacked, source_branch=source_branch,

            create_tree_if_local=create_tree_if_local)

    def _sprout(self, op, url, revision_id=None, force_new_repo=False,

               recurse='down', possible_transports=None,

               accelerator_tree=None, hardlink=False, stacked=False,

               source_branch=None, create_tree_if_local=True):

        add_cleanup = op.add_cleanup

        target_transport = get_transport(url, possible_transports)

        target_transport.ensure_base()

        cloning_format = self.cloning_metadir(stacked)

        # Create/update the result branch

        result = cloning_format.initialize_on_transport(target_transport)

        # if a stacked branch wasn't requested, we don't create one

        # even if the origin was stacked

        stacked_branch_url = None

        if source_branch is not None:

            add_cleanup(source_branch.lock_read().unlock)

            if stacked:

                stacked_branch_url = self.root_transport.base

            source_repository = source_branch.repository

        else:

            try:

                source_branch = self.open_branch()

                source_repository = source_branch.repository

                if stacked:

                    stacked_branch_url = self.root_transport.base

            except errors.NotBranchError:

                source_branch = None

                try:

                    source_repository = self.open_repository()

                except errors.NoRepositoryPresent:

                    source_repository = None

                else:

                    add_cleanup(source_repository.lock_read().unlock)

            else:

                add_cleanup(source_branch.lock_read().unlock)

        repository_policy = result.determine_repository_policy(

            force_new_repo, stacked_branch_url, require_stacking=stacked)

        result_repo, is_new_repo = repository_policy.acquire_repository()

        add_cleanup(result_repo.lock_write().unlock)

        is_stacked = stacked or (len(result_repo._fallback_repositories) != 0)

        if is_new_repo and revision_id is not None and not is_stacked:

            fetch_spec = graph.PendingAncestryResult(

                [revision_id], source_repository)

        else:

            fetch_spec = None

        if source_repository is not None:

            # Fetch while stacked to prevent unstacked fetch from

            # Branch.sprout.

            if fetch_spec is None:

                result_repo.fetch(source_repository, revision_id=revision_id)

            else:

                result_repo.fetch(source_repository, fetch_spec=fetch_spec)

        if source_branch is None:

            # this is for sprouting a controldir without a branch; is that

            # actually useful?

            # Not especially, but it's part of the contract.

            result_branch = result.create_branch()

        else:

            result_branch = source_branch.sprout(result,

                revision_id=revision_id, repository_policy=repository_policy,

                repository=result_repo)

        mutter("created new branch %r" % (result_branch,))

        # Create/update the result working tree

        if (create_tree_if_local and

            isinstance(target_transport, local.LocalTransport) and

            (result_repo is None or result_repo.make_working_trees())):

            wt = result.create_workingtree(accelerator_tree=accelerator_tree,

                hardlink=hardlink, from_branch=result_branch)

            wt.lock_write()

            try:

                if wt.path2id('') is None:

                    try:

                        wt.set_root_id(self.open_workingtree.get_root_id())

                    except errors.NoWorkingTree:

                        pass

            finally:

                wt.unlock()

        else:

            wt = None

        if recurse == 'down':

            if wt is not None:

                basis = wt.basis_tree()

                basis.lock_read()

                subtrees = basis.iter_references()

            elif result_branch is not None:

                basis = result_branch.basis_tree()

                basis.lock_read()

                subtrees = basis.iter_references()

            elif source_branch is not None:

                basis = source_branch.basis_tree()

                basis.lock_read()

                subtrees = basis.iter_references()

            else:

                subtrees = []

                basis = None

            try:

                for path, file_id in subtrees:

                    target = urlutils.join(url, urlutils.escape(path))

                    sublocation = source_branch.reference_parent(file_id, path)

                    sublocation.bzrdir.sprout(target,

                        basis.get_reference_revision(file_id, path),

                        force_new_repo=force_new_repo, recurse=recurse,

                        stacked=stacked)

            finally:

                if basis is not None:

                    basis.unlock()

        return result

    def push_branch(self, source, revision_id=None, overwrite=False, 

        remember=False, create_prefix=False):

        """Push the source branch into this ControlDir."""

        br_to = None

        # If we can open a branch, use its direct repository, otherwise see

        # if there is a repository without a branch.

        try:

            br_to = self.open_branch()

        except errors.NotBranchError:

            # Didn't find a branch, can we find a repository?

            repository_to = self.find_repository()

        else:

            # Found a branch, so we must have found a repository

            repository_to = br_to.repository

        push_result = PushResult()

        push_result.source_branch = source

        if br_to is None:

            # We have a repository but no branch, copy the revisions, and then

            # create a branch.

            repository_to.fetch(source.repository, revision_id=revision_id)

            br_to = source.clone(self, revision_id=revision_id)

            if source.get_push_location() is None or remember:

                source.set_push_location(br_to.base)

            push_result.stacked_on = None

            push_result.branch_push_result = None

            push_result.old_revno = None

            push_result.old_revid = _mod_revision.NULL_REVISION

            push_result.target_branch = br_to

            push_result.master_branch = None

            push_result.workingtree_updated = False

        else:

            # We have successfully opened the branch, remember if necessary:

            if source.get_push_location() is None or remember:

                source.set_push_location(br_to.base)

            try:

                tree_to = self.open_workingtree()

            except errors.NotLocalUrl:

                push_result.branch_push_result = source.push(br_to, 

                    overwrite, stop_revision=revision_id)

                push_result.workingtree_updated = False

            except errors.NoWorkingTree:

                push_result.branch_push_result = source.push(br_to,

                    overwrite, stop_revision=revision_id)

                push_result.workingtree_updated = None # Not applicable

            else:

                tree_to.lock_write()

                try:

                    push_result.branch_push_result = source.push(

                        tree_to.branch, overwrite, stop_revision=revision_id)

                    tree_to.update()

                finally:

                    tree_to.unlock()

                push_result.workingtree_updated = True

            push_result.old_revno = push_result.branch_push_result.old_revno

            push_result.old_revid = push_result.branch_push_result.old_revid

            push_result.target_branch = \

                push_result.branch_push_result.target_branch

        return push_result

    def _get_tree_branch(self, name=None):

        """Return the branch and tree, if any, for this bzrdir.

        :param name: Name of colocated branch to open.

        Return None for tree if not present or inaccessible.

        Raise NotBranchError if no branch is present.

        :return: (tree, branch)

        """

        try:

            tree = self.open_workingtree()

        except (errors.NoWorkingTree, errors.NotLocalUrl):

            tree = None

            branch = self.open_branch(name=name)

        else:

            if name is not None:

                branch = self.open_branch(name=name)

            else:

                branch = tree.branch

        return tree, branch

    def get_config(self):

        """Get configuration for this ControlDir."""

        raise NotImplementedError(self.get_config)

    def check_conversion_target(self, target_format):

        """Check that a bzrdir as a whole can be converted to a new format."""

        raise NotImplementedError(self.check_conversion_target)

    def clone(self, url, revision_id=None, force_new_repo=False,

              preserve_stacking=False):

        """Clone this bzrdir and its contents to url verbatim.

        :param url: The url create the clone at.  If url's last component does

            not exist, it will be created.

        :param revision_id: The tip revision-id to use for any branch or

            working tree.  If not None, then the clone operation may tune

            itself to download less data.

        :param force_new_repo: Do not use a shared repository for the target

                               even if one is available.

        :param preserve_stacking: When cloning a stacked branch, stack the

            new branch on top of the other branch's stacked-on branch.

        """

        return self.clone_on_transport(get_transport(url),

                                       revision_id=revision_id,

                                       force_new_repo=force_new_repo,

                                       preserve_stacking=preserve_stacking)

    def clone_on_transport(self, transport, revision_id=None,

        force_new_repo=False, preserve_stacking=False, stacked_on=None,

        create_prefix=False, use_existing_dir=True):

        """Clone this bzrdir and its contents to transport verbatim.

        :param transport: The transport for the location to produce the clone

            at.  If the target directory does not exist, it will be created.

        :param revision_id: The tip revision-id to use for any branch or

            working tree.  If not None, then the clone operation may tune

            itself to download less data.

        :param force_new_repo: Do not use a shared repository for the target,

                               even if one is available.

        :param preserve_stacking: When cloning a stacked branch, stack the

            new branch on top of the other branch's stacked-on branch.

        :param create_prefix: Create any missing directories leading up to

            to_transport.

        :param use_existing_dir: Use an existing directory if one exists.

        """

        raise NotImplementedError(self.clone_on_transport)

class ControlDirFormat(object):

    """An encapsulation of the initialization and open routines for a format.

    Formats provide three things:

     * An initialization routine,

     * a format string,

     * an open routine.

    Formats are placed in a dict by their format string for reference

    during controldir opening. These should be subclasses of ControlDirFormat

    for consistency.

    Once a format is deprecated, just deprecate the initialize and open

    methods on the format class. Do not deprecate the object, as the

    object will be created every system load.

    :cvar colocated_branches: Whether this formats supports colocated branches.

    :cvar supports_workingtrees: This control directory can co-exist with a

        working tree.

    """

    _default_format = None

    """The default format used for new control directories."""

    _formats = []

    """The registered control formats - .bzr, ....

    This is a list of ControlDirFormat objects.

    """

    _server_probers = []

    """The registered server format probers, e.g. RemoteBzrProber.

    This is a list of Prober-derived classes.

    """

    _probers = []

    """The registered format probers, e.g. BzrProber.

    This is a list of Prober-derived classes.

    """

    colocated_branches = False

    """Whether co-located branches are supported for this control dir format.

    """

    supports_workingtrees = True

    def get_format_description(self):

        """Return the short description for this format."""

        raise NotImplementedError(self.get_format_description)

    def get_converter(self, format=None):

        """Return the converter to use to convert controldirs needing converts.

        This returns a bzrlib.controldir.Converter object.

        This should return the best upgrader to step this format towards the

        current default format. In the case of plugins we can/should provide

        some means for them to extend the range of returnable converters.

        :param format: Optional format to override the default format of the

                       library.

        """

        raise NotImplementedError(self.get_converter)

    def is_supported(self):

        """Is this format supported?

        Supported formats must be initializable and openable.

        Unsupported formats may not support initialization or committing or

        some other features depending on the reason for not being supported.

        """

        return True

    def same_model(self, target_format):

        return (self.repository_format.rich_root_data ==

            target_format.rich_root_data)

    @classmethod

    def register_format(klass, format):

        """Register a format that does not use '.bzr' for its control dir.

        """

        klass._formats.append(format)

    @classmethod

    def register_prober(klass, prober):

        """Register a prober that can look for a control dir.

        """

        klass._probers.append(prober)

    @classmethod

    def unregister_prober(klass, prober):

        """Unregister a prober.

        """

        klass._probers.remove(prober)

    @classmethod

    def register_server_prober(klass, prober):

        """Register a control format prober for client-server environments.

        These probers will be used before ones registered with

        register_prober.  This gives implementations that decide to the

        chance to grab it before anything looks at the contents of the format

        file.

        """

        klass._server_probers.append(prober)

    def __str__(self):

        # Trim the newline

        return self.get_format_description().rstrip()

    @classmethod

    def unregister_format(klass, format):

        klass._formats.remove(format)

    @classmethod

    def known_formats(klass):

        """Return all the known formats.

        """

        return set(klass._formats)

    @classmethod

    def find_format(klass, transport, _server_formats=True):

        """Return the format present at transport."""

        if _server_formats:

            _probers = klass._server_probers + klass._probers

        else:

            _probers = klass._probers

        for prober_kls in _probers:

            prober = prober_kls()

            try:

                return prober.probe_transport(transport)

            except errors.NotBranchError:

                # this format does not find a control dir here.

                pass

        raise errors.NotBranchError(path=transport.base)

    def initialize(self, url, possible_transports=None):

        """Create a control dir at this url and return an opened copy.

        While not deprecated, this method is very specific and its use will

        lead to many round trips to setup a working environment. See

        initialize_on_transport_ex for a [nearly] all-in-one method.

        Subclasses should typically override initialize_on_transport

        instead of this method.

        """

        return self.initialize_on_transport(get_transport(url,

                                                          possible_transports))

    def initialize_on_transport(self, transport):

        """Initialize a new controldir in the base directory of a Transport."""

        raise NotImplementedError(self.initialize_on_transport)

    def initialize_on_transport_ex(self, transport, use_existing_dir=False,

        create_prefix=False, force_new_repo=False, stacked_on=None,

        stack_on_pwd=None, repo_format_name=None, make_working_trees=None,

        shared_repo=False, vfs_only=False):

        """Create this format on transport.

        The directory to initialize will be created.

        :param force_new_repo: Do not use a shared repository for the target,

                               even if one is available.

        :param create_prefix: Create any missing directories leading up to

            to_transport.

        :param use_existing_dir: Use an existing directory if one exists.

        :param stacked_on: A url to stack any created branch on, None to follow

            any target stacking policy.

        :param stack_on_pwd: If stack_on is relative, the location it is

            relative to.

        :param repo_format_name: If non-None, a repository will be

            made-or-found. Should none be found, or if force_new_repo is True

            the repo_format_name is used to select the format of repository to

            create.

        :param make_working_trees: Control the setting of make_working_trees

            for a new shared repository when one is made. None to use whatever

            default the format has.

        :param shared_repo: Control whether made repositories are shared or

            not.

        :param vfs_only: If True do not attempt to use a smart server

        :return: repo, controldir, require_stacking, repository_policy. repo is

            None if none was created or found, controldir is always valid.

            require_stacking is the result of examining the stacked_on

            parameter and any stacking policy found for the target.

        """

        raise NotImplementedError(self.initialize_on_transport_ex)

    def network_name(self):

        """A simple byte string uniquely identifying this format for RPC calls.

        Bzr control formats use this disk format string to identify the format

        over the wire. Its possible that other control formats have more

        complex detection requirements, so we permit them to use any unique and

        immutable string they desire.

        """

        raise NotImplementedError(self.network_name)

    def open(self, transport, _found=False):

        """Return an instance of this format for the dir transport points at.

        """

        raise NotImplementedError(self.open)

    @classmethod

    def _set_default_format(klass, format):

        """Set default format (for testing behavior of defaults only)"""

        klass._default_format = format

    @classmethod

    def get_default_format(klass):

        """Return the current default format."""

        return klass._default_format

class Prober(object):