Thuban/Model/save.py

# Copyright (c) 2001, 2002, 2003 by Intevation GmbH
# Authors:
# Jan-Oliver Wagner <[email protected]>
# Bernhard Herzog <[email protected]>
# Jonathan Coles <[email protected]>
#
# This program is free software under the GPL (>=v2)
# Read the file COPYING coming with Thuban for details.

"""
Functions to save a session to a file
"""

__version__ = "$Revision$"

import os

import Thuban.Lib.fileutil

from Thuban.Model.layer import Layer, RasterLayer

from Thuban.Model.classification import \
    ClassGroupDefault, ClassGroupSingleton, ClassGroupRange, ClassGroupMap
from Thuban.Model.transientdb import AutoTransientTable, TransientJoinedTable
from Thuban.Model.table import DBFTable, FIELDTYPE_STRING
from Thuban.Model.data import DerivedShapeStore, ShapefileStore

from Thuban.Model.xmlwriter import XMLWriter
from postgisdb import PostGISConnection, PostGISShapeStore

def relative_filename(dir, filename):
    """Return a filename relative to dir for the absolute file name absname.

    This is almost the same as the function in fileutil, except that dir
    can be an empty string in which case filename will be returned
    unchanged.
    """
    if dir:
        return Thuban.Lib.fileutil.relative_filename(dir, filename)
    else:
        return filename


def unify_filename(filename):
    """Return a 'unified' version of filename

    The .thuban files should be as platform independent as possible.
    Since they must contain filenames the filenames have to unified. We
    unify on unix-like filenames for now, which means we do nothing on a
    posix system and simply replace backslashes with slashes on windows
    """
    if os.name == "posix":
        return filename
    elif os.name == "nt":
        return "/".join(filename.split("\\"))
    else:
        raise RuntimeError("Unsupported platform for unify_filename: %s"
                           % os.name)

def sort_data_stores(stores):
    """Return a topologically sorted version of the sequence of data containers

    The list is sorted so that data containers that depend on other data
    containers have higher indexes than the containers they depend on.
    """
    if not stores:
        return []
    processed = {}
    result = []
    todo = stores[:]
    while todo:
        # It doesn't really matter which if the items of todo is
        # processed next, but if we take the first one, the order is
        # preserved to some degree which makes writing some of the test
        # cases easier.
        container = todo.pop(0)
        if id(container) in processed:
            continue
        deps = [dep for dep in container.Dependencies()
                    if id(dep) not in processed]
        if deps:
            todo.append(container)
            todo.extend(deps)
        else:
            result.append(container)
            processed[id(container)] = 1
    return result


class SessionSaver(XMLWriter):

    """Class to serialize a session into an XML file.

    Applications built on top of Thuban may derive from this class and
    override or extend the methods to save additional information. This
    additional information should take the form of additional attributes
    or elements whose names are prefixed with a namespace. To define a
    namespace derived classes should extend the write_session method to
    pass the namespaces to the default implementation.
    """


    def __init__(self, session):
        XMLWriter.__init__(self)
        self.session = session
        # Map object ids to the ids used in the thuban files
        self.idmap = {}

    def get_id(self, obj):
        """Return the id used in the thuban file for the object obj"""
        return self.idmap.get(id(obj))

    def define_id(self, obj, value = None):
        if value is None:
            value = "D" + str(id(obj))
        self.idmap[id(obj)] = value
        return value

    def has_id(self, obj):
        return self.idmap.has_key(id(obj))

    def prepare_filename(self, filename):
        """Return the string to use when writing filename to the thuban file

        The returned string is a unified version (only slashes as
        directory separators, see unify_filename) of filename expressed
        relative to the directory the .thuban file is written to.
        """
        return unify_filename(relative_filename(self.dir, filename))

    def write(self, file_or_filename):
        XMLWriter.write(self, file_or_filename)

        self.write_header("session", "thuban-1.0.dtd")
        self.write_session(self.session)
        self.close()

    def write_session(self, session, attrs = None, namespaces = ()):
        """Write the session and its contents

        By default, write a session element with the title attribute and
        call write_map for each map contained in the session.

        The optional argument attrs is for additional attributes and, if
        given, should be a mapping from attribute names to attribute
        values. The values should not be XML-escaped yet.

        The optional argument namespaces, if given, should be a sequence
        of (name, URI) pairs. The namespaces are written as namespace
        attributes into the session element. This is mainly useful for
        derived classes that need to store additional information in a
        thuban session file.
        """
        if attrs is None:
            attrs = {}
        attrs["title"] = session.title
        for name, uri in namespaces:
            attrs["xmlns:" + name] = uri
        # default name space
        attrs["xmlns"] = \
               "http://thuban.intevation.org/dtds/thuban-1.0-dev.dtd"
        self.open_element("session", attrs)
        self.write_db_connections(session)
        self.write_data_containers(session)
        for map in session.Maps():
            self.write_map(map)
        self.close_element("session")

    def write_db_connections(self, session):
        for conn in session.DBConnections():
            if isinstance(conn, PostGISConnection):
                self.write_element("dbconnection",
                                   {"id": self.define_id(conn),
                                    "dbtype": "postgis",
                                    "host": conn.host,
                                    "port": conn.port,
                                    "user": conn.user,
                                    "dbname": conn.dbname})
            else:
                raise ValueError("Can't handle db connection %r" % conn)

    def write_data_containers(self, session):
        containers = sort_data_stores(session.DataContainers())
        for container in containers:
            if isinstance(container, AutoTransientTable):
                # AutoTransientTable instances are invisible in the
                # thuban files. They're only used internally. To make
                # sure that containers depending on AutoTransientTable
                # instances refer to the right real containers we give
                # the AutoTransientTable instances the same id as the
                # source they depend on.
                self.define_id(container,
                               self.get_id(container.Dependencies()[0]))
                continue

            idvalue = self.define_id(container)
            if isinstance(container, ShapefileStore):
                self.define_id(container.Table(), idvalue)
                filename = self.prepare_filename(container.FileName())
                self.write_element("fileshapesource",
                                   {"id": idvalue, "filename": filename,
                                    "filetype": "shapefile"})
            elif isinstance(container, DerivedShapeStore):
                shapesource, table = container.Dependencies()
                self.write_element("derivedshapesource",
                                   {"id": idvalue,
                                    "shapesource": self.get_id(shapesource),
                                    "table": self.get_id(table)})
            elif isinstance(container, PostGISShapeStore):
                conn = container.DBConnection()
                self.write_element("dbshapesource",
                                   {"id": idvalue,
                                    "dbconn": self.get_id(conn),
                                    "tablename": container.TableName()})
            elif isinstance(container, DBFTable):
                filename = self.prepare_filename(container.FileName())
                self.write_element("filetable",
                                   {"id": idvalue,
                                    "title": container.Title(),
                                    "filename": filename,
                                    "filetype": "DBF"})
            elif isinstance(container, TransientJoinedTable):
                left, right = container.Dependencies()
                left_field = container.left_field
                right_field = container.right_field
                self.write_element("jointable",
                                   {"id": idvalue,
                                    "title": container.Title(),
                                    "right": self.get_id(right),
                                    "rightcolumn": right_field,
                                    "left": self.get_id(left),
                                    "leftcolumn": left_field,
                                    "jointype": container.JoinType()})
            else:
                raise ValueError("Can't handle container %r" % container)


    def write_map(self, map):
        """Write the map and its contents.

        By default, write a map element element with the title
        attribute, call write_projection to write the projection
        element, call write_layer for each layer contained in the map
        and finally call write_label_layer to write the label layer.
        """
        self.open_element('map title="%s"' % self.encode(map.title))
        self.write_projection(map.projection)
        for layer in map.Layers():
            self.write_layer(layer)
        self.write_label_layer(map.LabelLayer())
        self.close_element('map')

    def write_projection(self, projection):
        """Write the projection.
        """
        if projection and len(projection.params) > 0:
            attrs = {"name": projection.GetName()}
            epsg = projection.EPSGCode()
            if epsg is not None:
                attrs["epsg"] = epsg
            self.open_element("projection", attrs)
            for param in projection.params:
                self.write_element('parameter value="%s"' % 
                                   self.encode(param))
            self.close_element("projection")

    def write_layer(self, layer, attrs = None):
        """Write the layer.

        The optional argument attrs is for additional attributes and, if
        given, should be a mapping from attribute names to attribute
        values. The values should not be XML-escaped yet.
        """

        if attrs is None:
            attrs = {}

        attrs["title"]   = layer.title
        attrs["visible"] = ("false", "true")[int(layer.Visible())]

        if isinstance(layer, Layer):
            attrs["shapestore"]   = self.get_id(layer.ShapeStore())

            lc = layer.GetClassification()
            attrs["stroke"] = lc.GetDefaultLineColor().hex()
            attrs["stroke_width"] = str(lc.GetDefaultLineWidth())
            attrs["fill"] = lc.GetDefaultFill().hex()

            self.open_element("layer", attrs)
            self.write_projection(layer.GetProjection())
            self.write_classification(layer)
            self.close_element("layer")
        elif isinstance(layer, RasterLayer):
            attrs["filename"] = self.prepare_filename(layer.filename)
            self.open_element("rasterlayer", attrs)
            self.write_projection(layer.GetProjection())
            self.close_element("rasterlayer")

    def write_classification(self, layer, attrs = None):
        """Write Classification information."""

        if attrs is None:
            attrs = {}

        lc = layer.GetClassification()

        field = layer.GetClassificationColumn()

        #
        # there isn't a classification of anything so do nothing
        #
        if field is None: return

        attrs["field"] = field
        attrs["field_type"] = str(layer.GetFieldType(field))
        self.open_element("classification", attrs)

        for g in lc:
            if isinstance(g, ClassGroupDefault):
                open_el  = 'clnull label="%s"' % self.encode(g.GetLabel())
                close_el = 'clnull'
            elif isinstance(g, ClassGroupSingleton):
                if layer.GetFieldType(field) == FIELDTYPE_STRING:
                    value = self.encode(g.GetValue())
                else:
                    value = str(g.GetValue())
                open_el  = 'clpoint label="%s" value="%s"' \
                           % (self.encode(g.GetLabel()), value)
                close_el = 'clpoint'
            elif isinstance(g, ClassGroupRange):
                open_el  = 'clrange label="%s" range="%s"' \
                          % (self.encode(g.GetLabel()), str(g.GetRange()))
                close_el = 'clrange'
            else:
                assert False, _("Unsupported group type in classification")
                continue

            data = g.GetProperties()
            dict = {'stroke'      : data.GetLineColor().hex(),
                    'stroke_width': str(data.GetLineWidth()),
                    'fill'        : data.GetFill().hex()}

            self.open_element(open_el)
            self.write_element("cldata", dict)
            self.close_element(close_el)

        self.close_element("classification")

    def write_label_layer(self, layer):
        """Write the label layer.
        """
        labels = layer.Labels()
        if labels:
            self.open_element('labellayer')
            for label in labels:
                self.write_element(('label x="%g" y="%g" text="%s"'
                                    ' halign="%s" valign="%s"')
                                % (label.x, label.y, 
                                   self.encode(label.text), 
                                   label.halign,
                                   label.valign))
            self.close_element('labellayer')


def save_session(session, file, saver_class = None):
    """Save the session session to a file.

    The file argument may either be a filename or an open file object.

    The optional argument saver_class is the class to use to serialize
    the session. By default or if it's None, the saver class will be
    SessionSaver.

    If writing the session is successful call the session's
    UnsetModified method
    """
    if saver_class is None:
        saver_class = SessionSaver
    saver = saver_class(session)
    saver.write(file)

    # after a successful save consider the session unmodified.
    session.UnsetModified()
1	bh	454	# Copyright (c) 2001, 2002, 2003 by Intevation GmbH
2	bh	6	# Authors:
3			# Jan-Oliver Wagner <[email protected]>
4			# Bernhard Herzog <[email protected]>
5	jonathan	414	# Jonathan Coles <[email protected]>
6	bh	6	#
7			# This program is free software under the GPL (>=v2)
8			# Read the file COPYING coming with Thuban for details.
9
10			"""
11			Functions to save a session to a file
12			"""
13
14			__version__ = "$Revision$"
15
16			import os
17
18	bh	201	import Thuban.Lib.fileutil
19	bh	6
20	jonathan	932	from Thuban.Model.layer import Layer, RasterLayer
21
22	jonathan	876	from Thuban.Model.classification import \
23			ClassGroupDefault, ClassGroupSingleton, ClassGroupRange, ClassGroupMap
24	bh	1268	from Thuban.Model.transientdb import AutoTransientTable, TransientJoinedTable
25	bh	1417	from Thuban.Model.table import DBFTable, FIELDTYPE_STRING
26	bh	1268	from Thuban.Model.data import DerivedShapeStore, ShapefileStore
27	jonathan	429
28	jonathan	1160	from Thuban.Model.xmlwriter import XMLWriter
29	bh	1638	from postgisdb import PostGISConnection, PostGISShapeStore
30	jonathan	366
31	bh	201	def relative_filename(dir, filename):
32			"""Return a filename relative to dir for the absolute file name absname.
33
34			This is almost the same as the function in fileutil, except that dir
35			can be an empty string in which case filename will be returned
36			unchanged.
37			"""
38			if dir:
39			return Thuban.Lib.fileutil.relative_filename(dir, filename)
40			else:
41			return filename
42
43	bh	1268
44	bh	1989	def unify_filename(filename):
45			"""Return a 'unified' version of filename
46
47			The .thuban files should be as platform independent as possible.
48			Since they must contain filenames the filenames have to unified. We
49			unify on unix-like filenames for now, which means we do nothing on a
50			posix system and simply replace backslashes with slashes on windows
51			"""
52			if os.name == "posix":
53			return filename
54			elif os.name == "nt":
55			return "/".join(filename.split("\\"))
56			else:
57			raise RuntimeError("Unsupported platform for unify_filename: %s"
58			% os.name)
59
60	bh	1268	def sort_data_stores(stores):
61			"""Return a topologically sorted version of the sequence of data containers
62
63			The list is sorted so that data containers that depend on other data
64			containers have higher indexes than the containers they depend on.
65			"""
66			if not stores:
67			return []
68			processed = {}
69			result = []
70			todo = stores[:]
71			while todo:
72			# It doesn't really matter which if the items of todo is
73			# processed next, but if we take the first one, the order is
74			# preserved to some degree which makes writing some of the test
75			# cases easier.
76			container = todo.pop(0)
77			if id(container) in processed:
78			continue
79			deps = [dep for dep in container.Dependencies()
80			if id(dep) not in processed]
81			if deps:
82			todo.append(container)
83			todo.extend(deps)
84			else:
85			result.append(container)
86			processed[id(container)] = 1
87			return result
88
89
90	jonathan	710	class SessionSaver(XMLWriter):
91	bh	268
92	jonathan	697	"""Class to serialize a session into an XML file.
93
94			Applications built on top of Thuban may derive from this class and
95			override or extend the methods to save additional information. This
96			additional information should take the form of additional attributes
97			or elements whose names are prefixed with a namespace. To define a
98			namespace derived classes should extend the write_session method to
99			pass the namespaces to the default implementation.
100			"""
101
102
103			def __init__(self, session):
104	jonathan	710	XMLWriter.__init__(self)
105	jonathan	697	self.session = session
106	bh	1268	# Map object ids to the ids used in the thuban files
107			self.idmap = {}
108	jonathan	697
109	bh	1268	def get_id(self, obj):
110			"""Return the id used in the thuban file for the object obj"""
111			return self.idmap.get(id(obj))
112
113			def define_id(self, obj, value = None):
114			if value is None:
115			value = "D" + str(id(obj))
116			self.idmap[id(obj)] = value
117			return value
118
119			def has_id(self, obj):
120			return self.idmap.has_key(id(obj))
121
122	bh	1989	def prepare_filename(self, filename):
123			"""Return the string to use when writing filename to the thuban file
124
125			The returned string is a unified version (only slashes as
126			directory separators, see unify_filename) of filename expressed
127			relative to the directory the .thuban file is written to.
128			"""
129			return unify_filename(relative_filename(self.dir, filename))
130
131	jonathan	697	def write(self, file_or_filename):
132	jonathan	710	XMLWriter.write(self, file_or_filename)
133	jonathan	697
134	bh	1843	self.write_header("session", "thuban-1.0.dtd")
135	jonathan	697	self.write_session(self.session)
136			self.close()
137
138	bh	268	def write_session(self, session, attrs = None, namespaces = ()):
139			"""Write the session and its contents
140
141			By default, write a session element with the title attribute and
142			call write_map for each map contained in the session.
143
144			The optional argument attrs is for additional attributes and, if
145			given, should be a mapping from attribute names to attribute
146			values. The values should not be XML-escaped yet.
147
148			The optional argument namespaces, if given, should be a sequence
149			of (name, URI) pairs. The namespaces are written as namespace
150			attributes into the session element. This is mainly useful for
151			derived classes that need to store additional information in a
152			thuban session file.
153			"""
154			if attrs is None:
155			attrs = {}
156			attrs["title"] = session.title
157			for name, uri in namespaces:
158			attrs["xmlns:" + name] = uri
159	bh	1268	# default name space
160			attrs["xmlns"] = \
161	bh	1843	"http://thuban.intevation.org/dtds/thuban-1.0-dev.dtd"
162	jonathan	366	self.open_element("session", attrs)
163	bh	1638	self.write_db_connections(session)
164	bh	1268	self.write_data_containers(session)
165	bh	268	for map in session.Maps():
166			self.write_map(map)
167	jonathan	366	self.close_element("session")
168	bh	268
169	bh	1638	def write_db_connections(self, session):
170			for conn in session.DBConnections():
171			if isinstance(conn, PostGISConnection):
172			self.write_element("dbconnection",
173			{"id": self.define_id(conn),
174			"dbtype": "postgis",
175			"host": conn.host,
176			"port": conn.port,
177			"user": conn.user,
178			"dbname": conn.dbname})
179			else:
180			raise ValueError("Can't handle db connection %r" % conn)
181
182	bh	1268	def write_data_containers(self, session):
183			containers = sort_data_stores(session.DataContainers())
184			for container in containers:
185			if isinstance(container, AutoTransientTable):
186			# AutoTransientTable instances are invisible in the
187			# thuban files. They're only used internally. To make
188			# sure that containers depending on AutoTransientTable
189			# instances refer to the right real containers we give
190			# the AutoTransientTable instances the same id as the
191			# source they depend on.
192			self.define_id(container,
193			self.get_id(container.Dependencies()[0]))
194			continue
195
196			idvalue = self.define_id(container)
197			if isinstance(container, ShapefileStore):
198			self.define_id(container.Table(), idvalue)
199	bh	1989	filename = self.prepare_filename(container.FileName())
200	bh	1268	self.write_element("fileshapesource",
201			{"id": idvalue, "filename": filename,
202			"filetype": "shapefile"})
203			elif isinstance(container, DerivedShapeStore):
204			shapesource, table = container.Dependencies()
205			self.write_element("derivedshapesource",
206			{"id": idvalue,
207			"shapesource": self.get_id(shapesource),
208			"table": self.get_id(table)})
209	bh	1638	elif isinstance(container, PostGISShapeStore):
210			conn = container.DBConnection()
211			self.write_element("dbshapesource",
212			{"id": idvalue,
213			"dbconn": self.get_id(conn),
214			"tablename": container.TableName()})
215	bh	1268	elif isinstance(container, DBFTable):
216	bh	1989	filename = self.prepare_filename(container.FileName())
217	bh	1268	self.write_element("filetable",
218			{"id": idvalue,
219			"title": container.Title(),
220			"filename": filename,
221			"filetype": "DBF"})
222			elif isinstance(container, TransientJoinedTable):
223			left, right = container.Dependencies()
224			left_field = container.left_field
225			right_field = container.right_field
226			self.write_element("jointable",
227			{"id": idvalue,
228			"title": container.Title(),
229			"right": self.get_id(right),
230			"rightcolumn": right_field,
231			"left": self.get_id(left),
232	bh	1375	"leftcolumn": left_field,
233			"jointype": container.JoinType()})
234	bh	1268	else:
235			raise ValueError("Can't handle container %r" % container)
236
237
238	bh	268	def write_map(self, map):
239			"""Write the map and its contents.
240
241			By default, write a map element element with the title
242			attribute, call write_projection to write the projection
243			element, call write_layer for each layer contained in the map
244			and finally call write_label_layer to write the label layer.
245			"""
246	jonathan	876	self.open_element('map title="%s"' % self.encode(map.title))
247	bh	268	self.write_projection(map.projection)
248			for layer in map.Layers():
249			self.write_layer(layer)
250			self.write_label_layer(map.LabelLayer())
251	jonathan	366	self.close_element('map')
252	bh	6
253	bh	268	def write_projection(self, projection):
254			"""Write the projection.
255			"""
256			if projection and len(projection.params) > 0:
257	bh	1843	attrs = {"name": projection.GetName()}
258			epsg = projection.EPSGCode()
259			if epsg is not None:
260			attrs["epsg"] = epsg
261			self.open_element("projection", attrs)
262	bh	268	for param in projection.params:
263	jonathan	876	self.write_element('parameter value="%s"' %
264			self.encode(param))
265	jonathan	366	self.close_element("projection")
266	bh	268
267			def write_layer(self, layer, attrs = None):
268			"""Write the layer.
269
270			The optional argument attrs is for additional attributes and, if
271			given, should be a mapping from attribute names to attribute
272			values. The values should not be XML-escaped yet.
273			"""
274	jonathan	391
275	bh	268	if attrs is None:
276			attrs = {}
277	jonathan	429
278	jonathan	1251	attrs["title"] = layer.title
279			attrs["visible"] = ("false", "true")[int(layer.Visible())]
280	bh	268
281	jonathan	932	if isinstance(layer, Layer):
282	bh	1268	attrs["shapestore"] = self.get_id(layer.ShapeStore())
283	jonathan	740
284	jonathan	932	lc = layer.GetClassification()
285	bh	1268	attrs["stroke"] = lc.GetDefaultLineColor().hex()
286	jonathan	932	attrs["stroke_width"] = str(lc.GetDefaultLineWidth())
287	bh	1268	attrs["fill"] = lc.GetDefaultFill().hex()
288	jonathan	740
289	jonathan	932	self.open_element("layer", attrs)
290			self.write_projection(layer.GetProjection())
291			self.write_classification(layer)
292			self.close_element("layer")
293			elif isinstance(layer, RasterLayer):
294	bh	1989	attrs["filename"] = self.prepare_filename(layer.filename)
295	jonathan	932	self.open_element("rasterlayer", attrs)
296			self.write_projection(layer.GetProjection())
297			self.close_element("rasterlayer")
298
299	jonathan	366	def write_classification(self, layer, attrs = None):
300	jonathan	1251	"""Write Classification information."""
301
302	jonathan	366	if attrs is None:
303			attrs = {}
304
305	jonathan	414	lc = layer.GetClassification()
306	jonathan	366
307	bh	1452	field = layer.GetClassificationColumn()
308
309	jonathan	366	#
310	jonathan	1251	# there isn't a classification of anything so do nothing
311	jonathan	366	#
312			if field is None: return
313
314			attrs["field"] = field
315	jonathan	1430	attrs["field_type"] = str(layer.GetFieldType(field))
316	jonathan	366	self.open_element("classification", attrs)
317
318	jonathan	1251	for g in lc:
319			if isinstance(g, ClassGroupDefault):
320			open_el = 'clnull label="%s"' % self.encode(g.GetLabel())
321			close_el = 'clnull'
322	bh	1417	elif isinstance(g, ClassGroupSingleton):
323	jonathan	1430	if layer.GetFieldType(field) == FIELDTYPE_STRING:
324	bh	1417	value = self.encode(g.GetValue())
325			else:
326			value = str(g.GetValue())
327	jonathan	1251	open_el = 'clpoint label="%s" value="%s"' \
328	bh	1417	% (self.encode(g.GetLabel()), value)
329	jonathan	1251	close_el = 'clpoint'
330			elif isinstance(g, ClassGroupRange):
331			open_el = 'clrange label="%s" range="%s"' \
332			% (self.encode(g.GetLabel()), str(g.GetRange()))
333			close_el = 'clrange'
334			else:
335			assert False, _("Unsupported group type in classification")
336			continue
337	jonathan	429
338	jonathan	1251	data = g.GetProperties()
339			dict = {'stroke' : data.GetLineColor().hex(),
340			'stroke_width': str(data.GetLineWidth()),
341			'fill' : data.GetFill().hex()}
342	jonathan	429
343	jonathan	1251	self.open_element(open_el)
344			self.write_element("cldata", dict)
345			self.close_element(close_el)
346	jonathan	366
347			self.close_element("classification")
348
349	bh	268	def write_label_layer(self, layer):
350			"""Write the label layer.
351			"""
352			labels = layer.Labels()
353	bh	6	if labels:
354	jonathan	366	self.open_element('labellayer')
355	bh	6	for label in labels:
356	jonathan	366	self.write_element(('label x="%g" y="%g" text="%s"'
357			' halign="%s" valign="%s"')
358	jonathan	876	% (label.x, label.y,
359			self.encode(label.text),
360			label.halign,
361	bh	268	label.valign))
362	jonathan	366	self.close_element('labellayer')
363	bh	6
364	bh	268
365
366			def save_session(session, file, saver_class = None):
367			"""Save the session session to a file.
368
369			The file argument may either be a filename or an open file object.
370
371			The optional argument saver_class is the class to use to serialize
372			the session. By default or if it's None, the saver class will be
373	jonathan	697	SessionSaver.
374	bh	268
375			If writing the session is successful call the session's
376			UnsetModified method
377			"""
378			if saver_class is None:
379	jonathan	697	saver_class = SessionSaver
380	bh	268	saver = saver_class(session)
381			saver.write(file)
382
383	bh	6	# after a successful save consider the session unmodified.
384			session.UnsetModified()
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