[rql rewriting] handle case where we've and optional inlined relation in the original query. Also, we should append EXISTS even in subquery to avoid inserting duplicates in results
"""contains utility functions and some visual component to restrict results of
a search
:organization: Logilab
:copyright: 2008-2010 LOGILAB S.A. (Paris, FRANCE), license is LGPL v2.
:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr
:license: GNU Lesser General Public License, v2.1 - http://www.gnu.org/licenses
"""
__docformat__ = "restructuredtext en"
from itertools import chain
from copy import deepcopy
from datetime import date, datetime, timedelta
from logilab.mtconverter import xml_escape
from logilab.common.graph import has_path
from logilab.common.decorators import cached
from logilab.common.date import datetime2ticks
from logilab.common.compat import all
from rql import parse, nodes
from cubicweb import Unauthorized, typed_eid
from cubicweb.schema import display_name
from cubicweb.utils import make_uid
from cubicweb.selectors import match_context_prop, partial_relation_possible
from cubicweb.appobject import AppObject
from cubicweb.web.htmlwidgets import HTMLWidget
## rqlst manipulation functions used by facets ################################
def prepare_facets_rqlst(rqlst, args=None):
"""prepare a syntax tree to generate facet filters
* remove ORDERBY clause
* cleanup selection (remove everything)
* undefine unnecessary variables
* set DISTINCT
* unset LIMIT/OFFSET
"""
if len(rqlst.children) > 1:
raise NotImplementedError('FIXME: union not yet supported')
select = rqlst.children[0]
mainvar = filtered_variable(select)
select.set_limit(None)
select.set_offset(None)
baserql = select.as_string(kwargs=args)
# cleanup sort terms
select.remove_sort_terms()
# selection: only vocabulary entity
for term in select.selection[:]:
select.remove_selected(term)
# remove unbound variables which only have some type restriction
for dvar in select.defined_vars.values():
if not (dvar is mainvar or dvar.stinfo['relations']):
select.undefine_variable(dvar)
# global tree config: DISTINCT, LIMIT, OFFSET
select.set_distinct(True)
return mainvar, baserql
def filtered_variable(rqlst):
vref = rqlst.selection[0].iget_nodes(nodes.VariableRef).next()
return vref.variable
def get_facet(req, facetid, rqlst, mainvar):
return req.vreg['facets'].object_by_id(facetid, req, rqlst=rqlst,
filtered_variable=mainvar)
def filter_hiddens(w, **kwargs):
for key, val in kwargs.items():
w(u'<input type="hidden" name="%s" value="%s" />' % (
key, xml_escape(val)))
def _may_be_removed(rel, schema, mainvar):
"""if the given relation may be removed from the tree, return the variable
on the other side of `mainvar`, else return None
Conditions:
* the relation is an attribute selection of the main variable
* the relation is optional relation linked to the main variable
* the relation is a mandatory relation linked to the main variable
without any restriction on the other variable
"""
lhs, rhs = rel.get_variable_parts()
rschema = schema.rschema(rel.r_type)
if lhs.variable is mainvar:
try:
ovar = rhs.variable
except AttributeError:
# constant restriction
# XXX: X title LOWER(T) if it makes sense?
return None
if rschema.final:
if len(ovar.stinfo['relations']) == 1:
# attribute selection
return ovar
return None
opt = 'right'
cardidx = 0
elif getattr(rhs, 'variable', None) is mainvar:
ovar = lhs.variable
opt = 'left'
cardidx = 1
else:
# not directly linked to the main variable
return None
if rel.optional in (opt, 'both'):
# optional relation
return ovar
if all(rdef.cardinality[cardidx] in '1+'
for rdef in rschema.rdefs.values()):
# mandatory relation without any restriction on the other variable
for orel in ovar.stinfo['relations']:
if rel is orel:
continue
if _may_be_removed(orel, schema, ovar) is None:
return None
return ovar
return None
def _add_rtype_relation(rqlst, mainvar, rtype, role):
"""add a relation relying `mainvar` to entities linked by the `rtype`
relation (where `mainvar` has `role`)
return the inserted variable for linked entities.
"""
newvar = rqlst.make_variable()
if role == 'object':
rqlst.add_relation(newvar, rtype, mainvar)
else:
rqlst.add_relation(mainvar, rtype, newvar)
return newvar
def _prepare_vocabulary_rqlst(rqlst, mainvar, rtype, role):
"""prepare a syntax tree to generate a filter vocabulary rql using the given
relation:
* create a variable to filter on this relation
* add the relation
* add the new variable to GROUPBY clause if necessary
* add the new variable to the selection
"""
newvar = _add_rtype_relation(rqlst, mainvar, rtype, role)
if rqlst.groupby:
rqlst.add_group_var(newvar)
rqlst.add_selected(newvar)
return newvar
def _remove_relation(rqlst, rel, var):
"""remove a constraint relation from the syntax tree"""
# remove the relation
rqlst.remove_node(rel)
# remove relations where the filtered variable appears on the
# lhs and rhs is a constant restriction
extra = []
for vrel in var.stinfo['relations']:
if vrel is rel:
continue
if vrel.children[0].variable is var:
if not vrel.children[1].get_nodes(nodes.Constant):
extra.append(vrel)
rqlst.remove_node(vrel)
return extra
def _set_orderby(rqlst, newvar, sortasc, sortfuncname):
if sortfuncname is None:
rqlst.add_sort_var(newvar, sortasc)
else:
vref = nodes.variable_ref(newvar)
vref.register_reference()
sortfunc = nodes.Function(sortfuncname)
sortfunc.append(vref)
term = nodes.SortTerm(sortfunc, sortasc)
rqlst.add_sort_term(term)
def insert_attr_select_relation(rqlst, mainvar, rtype, role, attrname,
sortfuncname=None, sortasc=True):
"""modify a syntax tree to :
* link a new variable to `mainvar` through `rtype` (where mainvar has `role`)
* retrieve only the newly inserted variable and its `attrname`
Sorting:
* on `attrname` ascendant (`sortasc`=True) or descendant (`sortasc`=False)
* on `sortfuncname`(`attrname`) if `sortfuncname` is specified
* no sort if `sortasc` is None
"""
_cleanup_rqlst(rqlst, mainvar)
var = _prepare_vocabulary_rqlst(rqlst, mainvar, rtype, role)
# not found, create one
attrvar = rqlst.make_variable()
rqlst.add_relation(var, attrname, attrvar)
# if query is grouped, we have to add the attribute variable
if rqlst.groupby:
if not attrvar in rqlst.groupby:
rqlst.add_group_var(attrvar)
if sortasc is not None:
_set_orderby(rqlst, attrvar, sortasc, sortfuncname)
# add attribute variable to selection
rqlst.add_selected(attrvar)
# add is restriction if necessary
if not mainvar.stinfo['typerels']:
etypes = frozenset(sol[mainvar.name] for sol in rqlst.solutions)
rqlst.add_type_restriction(mainvar, etypes)
return var
def _cleanup_rqlst(rqlst, mainvar):
"""cleanup tree from unnecessary restriction:
* attribute selection
* optional relations linked to the main variable
* mandatory relations linked to the main variable
"""
if rqlst.where is None:
return
schema = rqlst.root.schema
toremove = set()
vargraph = deepcopy(rqlst.vargraph) # graph representing links between variable
for rel in rqlst.where.get_nodes(nodes.Relation):
ovar = _may_be_removed(rel, schema, mainvar)
if ovar is not None:
toremove.add(ovar)
removed = set()
while toremove:
trvar = toremove.pop()
trvarname = trvar.name
# remove paths using this variable from the graph
linkedvars = vargraph.pop(trvarname)
for ovarname in linkedvars:
vargraph[ovarname].remove(trvarname)
# remove relation using this variable
for rel in chain(trvar.stinfo['relations'], trvar.stinfo['typerels']):
if rel in removed:
# already removed
continue
rqlst.remove_node(rel)
removed.add(rel)
# cleanup groupby clause
if rqlst.groupby:
for vref in rqlst.groupby[:]:
if vref.name == trvarname:
rqlst.remove_group_var(vref)
# we can also remove all variables which are linked to this variable
# and have no path to the main variable
for ovarname in linkedvars:
if ovarname == mainvar.name:
continue
if not has_path(vargraph, ovarname, mainvar.name):
toremove.add(rqlst.defined_vars[ovarname])
## base facet classes #########################################################
class AbstractFacet(AppObject):
__abstract__ = True
__registry__ = 'facets'
cw_property_defs = {
_('visible'): dict(type='Boolean', default=True,
help=_('display the box or not')),
_('order'): dict(type='Int', default=99,
help=_('display order of the box')),
_('context'): dict(type='String', default='',
# None <-> both
vocabulary=(_('tablefilter'), _('facetbox'), ''),
help=_('context where this box should be displayed')),
}
visible = True
context = ''
needs_update = False
start_unfolded = True
cw_rset = None # ensure facets have a cw_rset attribute
def __init__(self, req, rqlst=None, filtered_variable=None,
**kwargs):
super(AbstractFacet, self).__init__(req, **kwargs)
assert rqlst is not None
assert filtered_variable
# take care: facet may be retreived using `object_by_id` from an ajax call
# or from `select` using the result set to filter
self.rqlst = rqlst
self.filtered_variable = filtered_variable
@property
def operator(self):
# OR between selected values by default
return self._cw.form.get(self.__regid__ + '_andor', 'OR')
def get_widget(self):
"""return the widget instance to use to display this facet
"""
raise NotImplementedError
def add_rql_restrictions(self):
"""add restriction for this facet into the rql syntax tree"""
raise NotImplementedError
class VocabularyFacet(AbstractFacet):
needs_update = True
def get_widget(self):
"""return the widget instance to use to display this facet
default implentation expects a .vocabulary method on the facet and
return a combobox displaying this vocabulary
"""
vocab = self.vocabulary()
if len(vocab) <= 1:
return None
wdg = FacetVocabularyWidget(self)
selected = frozenset(typed_eid(eid) for eid in self._cw.list_form_param(self.__regid__))
for label, value in vocab:
if value is None:
wdg.append(FacetSeparator(label))
else:
wdg.append(FacetItem(self._cw, label, value, value in selected))
return wdg
def vocabulary(self):
"""return vocabulary for this facet, eg a list of 2-uple (label, value)
"""
raise NotImplementedError
def possible_values(self):
"""return a list of possible values (as string since it's used to
compare to a form value in javascript) for this facet
"""
raise NotImplementedError
def support_and(self):
return False
def rqlexec(self, rql, args=None, cachekey=None):
try:
return self._cw.execute(rql, args, cachekey)
except Unauthorized:
return []
class RelationFacet(VocabularyFacet):
__select__ = partial_relation_possible() & match_context_prop()
# class attributes to configure the rel ation facet
rtype = None
role = 'subject'
target_attr = 'eid'
# set this to a stored procedure name if you want to sort on the result of
# this function's result instead of direct value
sortfunc = None
# ascendant/descendant sorting
sortasc = True
# if you want to call a view on the entity instead of using `target_attr`
label_vid = None
@property
def title(self):
return display_name(self._cw, self.rtype, form=self.role)
def vocabulary(self):
"""return vocabulary for this facet, eg a list of 2-uple (label, value)
"""
rqlst = self.rqlst
rqlst.save_state()
if self.label_vid is not None and self.sortfunc is None:
sort = None # will be sorted on label
else:
sort = self.sortasc
try:
mainvar = self.filtered_variable
insert_attr_select_relation(rqlst, mainvar, self.rtype, self.role,
self.target_attr, self.sortfunc, sort)
try:
rset = self.rqlexec(rqlst.as_string(), self.cw_rset.args, self.cw_rset.cachekey)
except:
self.exception('error while getting vocabulary for %s, rql: %s',
self, rqlst.as_string())
return ()
finally:
rqlst.recover()
return self.rset_vocabulary(rset)
def possible_values(self):
"""return a list of possible values (as string since it's used to
compare to a form value in javascript) for this facet
"""
rqlst = self.rqlst
rqlst.save_state()
try:
_cleanup_rqlst(rqlst, self.filtered_variable)
_prepare_vocabulary_rqlst(rqlst, self.filtered_variable, self.rtype, self.role)
return [str(x) for x, in self.rqlexec(rqlst.as_string())]
finally:
rqlst.recover()
def rset_vocabulary(self, rset):
if self.label_vid is None:
_ = self._cw._
return [(_(label), eid) for eid, label in rset]
if self.sortfunc is None:
return sorted((entity.view(self.label_vid), entity.eid)
for entity in rset.entities())
return [(entity.view(self.label_vid), entity.eid)
for entity in rset.entities()]
@cached
def support_and(self):
rschema = self._cw.vreg.schema.rschema(self.rtype)
# XXX when called via ajax, no rset to compute possible types
possibletypes = self.cw_rset and self.cw_rset.column_types(0)
for rdef in rschema.rdefs.itervalues():
if possibletypes is not None:
if self.role == 'subject':
if not rdef.subject in possibletypes:
continue
elif not rdef.object in possibletypes:
continue
if rdef.role_cardinality(self.role) in '+*':
return True
return False
def add_rql_restrictions(self):
"""add restriction for this facet into the rql syntax tree"""
value = self._cw.form.get(self.__regid__)
if not value:
return
mainvar = self.filtered_variable
restrvar = _add_rtype_relation(self.rqlst, mainvar, self.rtype, self.role)
if isinstance(value, basestring):
# only one value selected
self.rqlst.add_eid_restriction(restrvar, value)
elif self.operator == 'OR':
# multiple values with OR operator
# set_distinct only if rtype cardinality is > 1
if self.support_and():
self.rqlst.set_distinct(True)
self.rqlst.add_eid_restriction(restrvar, value)
else:
# multiple values with AND operator
self.rqlst.add_eid_restriction(restrvar, value.pop())
while value:
restrvar = _add_rtype_relation(self.rqlst, mainvar, self.rtype, self.role)
self.rqlst.add_eid_restriction(restrvar, value.pop())
class AttributeFacet(RelationFacet):
# attribute type
attrtype = 'String'
# type of comparison: default is an exact match on the attribute value
comparator = '=' # could be '<', '<=', '>', '>='
def vocabulary(self):
"""return vocabulary for this facet, eg a list of 2-uple (label, value)
"""
rqlst = self.rqlst
rqlst.save_state()
try:
mainvar = self.filtered_variable
_cleanup_rqlst(rqlst, mainvar)
newvar = _prepare_vocabulary_rqlst(rqlst, mainvar, self.rtype, self.role)
_set_orderby(rqlst, newvar, self.sortasc, self.sortfunc)
try:
rset = self.rqlexec(rqlst.as_string(), self.cw_rset.args, self.cw_rset.cachekey)
except:
self.exception('error while getting vocabulary for %s, rql: %s',
self, rqlst.as_string())
return ()
finally:
rqlst.recover()
return self.rset_vocabulary(rset)
def rset_vocabulary(self, rset):
_ = self._cw._
return [(_(value), value) for value, in rset]
def support_and(self):
return False
def add_rql_restrictions(self):
"""add restriction for this facet into the rql syntax tree"""
value = self._cw.form.get(self.__regid__)
if not value:
return
mainvar = self.filtered_variable
self.rqlst.add_constant_restriction(mainvar, self.rtype, value,
self.attrtype, self.comparator)
class FilterRQLBuilder(object):
"""called by javascript to get a rql string from filter form"""
def __init__(self, req):
self._cw = req
def build_rql(self):#, tablefilter=False):
form = self._cw.form
facetids = form['facets'].split(',')
select = parse(form['baserql']).children[0] # XXX Union unsupported yet
mainvar = filtered_variable(select)
toupdate = []
for facetid in facetids:
facet = get_facet(self._cw, facetid, select, mainvar)
facet.add_rql_restrictions()
if facet.needs_update:
toupdate.append(facetid)
return select.as_string(), toupdate
class RangeFacet(AttributeFacet):
attrtype = 'Float' # only numerical types are supported
@property
def wdgclass(self):
return FacetRangeWidget
def get_widget(self):
"""return the widget instance to use to display this facet"""
values = set(value for _, value in self.vocabulary() if value is not None)
# Rset with entities (the facet is selected) but without values
if len(values) == 0:
return None
return self.wdgclass(self, min(values), max(values))
def infvalue(self):
return self._cw.form.get('%s_inf' % self.__regid__)
def supvalue(self):
return self._cw.form.get('%s_sup' % self.__regid__)
def formatvalue(self, value):
"""format `value` before in order to insert it in the RQL query"""
return unicode(value)
def add_rql_restrictions(self):
infvalue = self.infvalue()
if infvalue is None: # nothing sent
return
supvalue = self.supvalue()
self.rqlst.add_constant_restriction(self.filtered_variable,
self.rtype,
self.formatvalue(infvalue),
self.attrtype, '>=')
self.rqlst.add_constant_restriction(self.filtered_variable,
self.rtype,
self.formatvalue(supvalue),
self.attrtype, '<=')
class DateRangeFacet(RangeFacet):
attrtype = 'Date' # only date types are supported
@property
def wdgclass(self):
return DateFacetRangeWidget
def formatvalue(self, value):
"""format `value` before in order to insert it in the RQL query"""
return '"%s"' % date.fromtimestamp(float(value) / 1000).strftime('%Y/%m/%d')
class HasRelationFacet(AbstractFacet):
rtype = None # override me in subclass
role = 'subject' # role of filtered entity in the relation
@property
def title(self):
return display_name(self._cw, self.rtype, self.role)
def support_and(self):
return False
def get_widget(self):
return CheckBoxFacetWidget(self._cw, self,
'%s:%s' % (self.rtype, self),
self._cw.form.get(self.__regid__))
def add_rql_restrictions(self):
"""add restriction for this facet into the rql syntax tree"""
self.rqlst.set_distinct(True) # XXX
value = self._cw.form.get(self.__regid__)
if not value: # no value sent for this facet
return
var = self.rqlst.make_variable()
if self.role == 'subject':
self.rqlst.add_relation(self.filtered_variable, self.rtype, var)
else:
self.rqlst.add_relation(var, self.rtype, self.filtered_variable)
## html widets ################################################################
class FacetVocabularyWidget(HTMLWidget):
def __init__(self, facet):
self.facet = facet
self.items = []
def append(self, item):
self.items.append(item)
def _render(self):
title = xml_escape(self.facet.title)
facetid = xml_escape(self.facet.__regid__)
self.w(u'<div id="%s" class="facet">\n' % facetid)
self.w(u'<div class="facetTitle" cubicweb:facetName="%s">%s</div>\n' %
(xml_escape(facetid), title))
if self.facet.support_and():
_ = self.facet._cw._
self.w(u'''<select name="%s" class="radio facetOperator" title="%s">
<option value="OR">%s</option>
<option value="AND">%s</option>
</select>''' % (facetid + '_andor', _('and/or between different values'),
_('OR'), _('AND')))
cssclass = ''
if not self.facet.start_unfolded:
cssclass += ' hidden'
if len(self.items) > 6:
cssclass += ' overflowed'
self.w(u'<div class="facetBody%s">\n' % cssclass)
for item in self.items:
item.render(w=self.w)
self.w(u'</div>\n')
self.w(u'</div>\n')
class FacetStringWidget(HTMLWidget):
def __init__(self, facet):
self.facet = facet
self.value = None
def _render(self):
title = xml_escape(self.facet.title)
facetid = xml_escape(self.facet.__regid__)
self.w(u'<div id="%s" class="facet">\n' % facetid)
self.w(u'<div class="facetTitle" cubicweb:facetName="%s">%s</div>\n' %
(facetid, title))
self.w(u'<input name="%s" type="text" value="%s" />\n' % (facetid, self.value or u''))
self.w(u'</div>\n')
class FacetRangeWidget(HTMLWidget):
formatter = 'function (value) {return value;}'
onload = u'''
var _formatter = %(formatter)s;
jQuery("#%(sliderid)s").slider({
range: true,
min: %(minvalue)s,
max: %(maxvalue)s,
values: [%(minvalue)s, %(maxvalue)s],
stop: function(event, ui) { // submit when the user stops sliding
var form = $('#%(sliderid)s').closest('form');
buildRQL.apply(null, evalJSON(form.attr('cubicweb:facetargs')));
},
slide: function(event, ui) {
jQuery('#%(sliderid)s_inf').html(_formatter(ui.values[0]));
jQuery('#%(sliderid)s_sup').html(_formatter(ui.values[1]));
jQuery('input[name=%(facetid)s_inf]').val(ui.values[0]);
jQuery('input[name=%(facetid)s_sup]').val(ui.values[1]);
}
});
// use JS formatter to format value on page load
jQuery('#%(sliderid)s_inf').html(_formatter(jQuery('input[name=%(facetid)s_inf]').val()));
jQuery('#%(sliderid)s_sup').html(_formatter(jQuery('input[name=%(facetid)s_sup]').val()));
'''
#'# make emacs happier
def __init__(self, facet, minvalue, maxvalue):
self.facet = facet
self.minvalue = minvalue
self.maxvalue = maxvalue
def _render(self):
facet = self.facet
facet._cw.add_js('ui.slider.js')
facet._cw.add_css('ui.all.css')
sliderid = make_uid('theslider')
facetid = xml_escape(self.facet.__regid__)
facet._cw.html_headers.add_onload(self.onload % {
'sliderid': sliderid,
'facetid': facetid,
'minvalue': self.minvalue,
'maxvalue': self.maxvalue,
'formatter': self.formatter,
})
title = xml_escape(self.facet.title)
self.w(u'<div id="%s" class="facet">\n' % facetid)
self.w(u'<div class="facetTitle" cubicweb:facetName="%s">%s</div>\n' %
(facetid, title))
self.w(u'<span id="%s_inf"></span> - <span id="%s_sup"></span>'
% (sliderid, sliderid))
self.w(u'<input type="hidden" name="%s_inf" value="%s" />'
% (facetid, self.minvalue))
self.w(u'<input type="hidden" name="%s_sup" value="%s" />'
% (facetid, self.maxvalue))
self.w(u'<div id="%s"></div>' % sliderid)
self.w(u'</div>\n')
class DateFacetRangeWidget(FacetRangeWidget):
formatter = 'function (value) {return (new Date(parseFloat(value))).strftime(DATE_FMT);}'
def round_max_value(self, d):
'round to upper value to avoid filtering out the max value'
return datetime(d.year, d.month, d.day) + timedelta(days=1)
def __init__(self, facet, minvalue, maxvalue):
maxvalue = self.round_max_value(maxvalue)
super(DateFacetRangeWidget, self).__init__(facet,
datetime2ticks(minvalue),
datetime2ticks(maxvalue))
fmt = facet._cw.property_value('ui.date-format')
facet._cw.html_headers.define_var('DATE_FMT', fmt)
class FacetItem(HTMLWidget):
selected_img = "black-check.png"
unselected_img = "no-check-no-border.png"
def __init__(self, req, label, value, selected=False):
self._cw = req
self.label = label
self.value = value
self.selected = selected
def _render(self):
if self.selected:
cssclass = ' facetValueSelected'
imgsrc = self._cw.datadir_url + self.selected_img
imgalt = self._cw._('selected')
else:
cssclass = ''
imgsrc = self._cw.datadir_url + self.unselected_img
imgalt = self._cw._('not selected')
self.w(u'<div class="facetValue facetCheckBox%s" cubicweb:value="%s">\n'
% (cssclass, xml_escape(unicode(self.value))))
self.w(u'<img src="%s" alt="%s"/> ' % (imgsrc, imgalt))
self.w(u'<a href="javascript: {}">%s</a>' % xml_escape(self.label))
self.w(u'</div>')
class CheckBoxFacetWidget(HTMLWidget):
selected_img = "black-check.png"
unselected_img = "black-uncheck.png"
def __init__(self, req, facet, value, selected):
self._cw = req
self.facet = facet
self.value = value
self.selected = selected
def _render(self):
title = xml_escape(self.facet.title)
facetid = xml_escape(self.facet.__regid__)
self.w(u'<div id="%s" class="facet">\n' % facetid)
if self.selected:
cssclass = ' facetValueSelected'
imgsrc = self._cw.datadir_url + self.selected_img
imgalt = self._cw._('selected')
else:
cssclass = ''
imgsrc = self._cw.datadir_url + self.unselected_img
imgalt = self._cw._('not selected')
self.w(u'<div class="facetValue facetCheckBox%s" cubicweb:value="%s">\n'
% (cssclass, xml_escape(unicode(self.value))))
self.w(u'<div class="facetCheckBoxWidget">')
self.w(u'<img src="%s" alt="%s" cubicweb:unselimg="true" /> ' % (imgsrc, imgalt))
self.w(u'<label class="facetTitle" cubicweb:facetName="%s"><a href="javascript: {}">%s</a></label>' % (facetid, title))
self.w(u'</div>\n')
self.w(u'</div>\n')
self.w(u'</div>\n')
class FacetSeparator(HTMLWidget):
def __init__(self, label=None):
self.label = label or u' '
def _render(self):
pass