text: """Default tags used by the template system, available to all templates."""
  
  import sys
  import re
  from datetime import datetime
  from itertools import groupby, cycle as itertools_cycle
  
  from django.conf import settings
  from django.template.base import (Node, NodeList, Template, Library,
      TemplateSyntaxError, VariableDoesNotExist, InvalidTemplateLibrary,
      BLOCK_TAG_START, BLOCK_TAG_END, VARIABLE_TAG_START, VARIABLE_TAG_END,
      SINGLE_BRACE_START, SINGLE_BRACE_END, COMMENT_TAG_START, COMMENT_TAG_END,
      VARIABLE_ATTRIBUTE_SEPARATOR, get_library, token_kwargs, kwarg_re)
  from django.template.smartif import IfParser, Literal
  from django.template.defaultfilters import date
  from django.utils.encoding import smart_str, smart_unicode
  from django.utils.safestring import mark_safe
  from django.utils import timezone
  
  register = Library()
  
  class AutoEscapeControlNode(Node):
      """Implements the actions of the autoescape tag."""
      def __init__(self, setting, nodelist):
          self.setting, self.nodelist = setting, nodelist
  
      def render(self, context):
          old_setting = context.autoescape
          context.autoescape = self.setting
          output = self.nodelist.render(context)
          context.autoescape = old_setting
          if self.setting:
              return mark_safe(output)
          else:
              return output
  
  class CommentNode(Node):
      def render(self, context):
          return ''
  
  class CsrfTokenNode(Node):
      def render(self, context):
          csrf_token = context.get('csrf_token', None)
          if csrf_token:
              if csrf_token == 'NOTPROVIDED':
                  return mark_safe(u"")
              else:
                  return mark_safe(u"<div style='display:none'><input type='hidden' name='csrfmiddlewaretoken' value='%s' /></div>" % csrf_token)
          else:
              # It's very probable that the token is missing because of
              # misconfiguration, so we raise a warning
              from django.conf import settings
              if settings.DEBUG:
                  import warnings
                  warnings.warn("A {% csrf_token %} was used in a template, but the context did not provide the value.  This is usually caused by not using RequestContext.")
              return u''
  
  class CycleNode(Node):
      def __init__(self, cyclevars, variable_name=None, silent=False):
          self.cyclevars = cyclevars
          self.variable_name = variable_name
          self.silent = silent
  
      def render(self, context):
          if self not in context.render_context:
              # First time the node is rendered in template
              context.render_context[self] = itertools_cycle(self.cyclevars)
          cycle_iter = context.render_context[self]
          value = cycle_iter.next().resolve(context)
          if self.variable_name:
              context[self.variable_name] = value
          if self.silent:
              return ''
          return value
  
  class DebugNode(Node):
      def render(self, context):
          from pprint import pformat
          output = [pformat(val) for val in context]
          output.append('\n\n')
          output.append(pformat(sys.modules))
          return ''.join(output)
  
  class FilterNode(Node):
      def __init__(self, filter_expr, nodelist):
          self.filter_expr, self.nodelist = filter_expr, nodelist
  
      def render(self, context):
          output = self.nodelist.render(context)
          # Apply filters.
          context.update({'var': output})
          filtered = self.filter_expr.resolve(context)
          context.pop()
          return filtered
  
  class FirstOfNode(Node):
      def __init__(self, vars):
          self.vars = vars
  
      def render(self, context):
          for var in self.vars:
              value = var.resolve(context, True)
              if value:
                  return smart_unicode(value)
          return u''
  
  class ForNode(Node):
      child_nodelists = ('nodelist_loop', 'nodelist_empty')
  
      def __init__(self, loopvars, sequence, is_reversed, nodelist_loop, nodelist_empty=None):
          self.loopvars, self.sequence = loopvars, sequence
          self.is_reversed = is_reversed
          self.nodelist_loop = nodelist_loop
          if nodelist_empty is None:
              self.nodelist_empty = NodeList()
          else:
              self.nodelist_empty = nodelist_empty
  
      def __repr__(self):
          reversed_text = self.is_reversed and ' reversed' or ''
          return "<For Node: for %s in %s, tail_len: %d%s>" % \
              (', '.join(self.loopvars), self.sequence, len(self.nodelist_loop),
               reversed_text)
  
      def __iter__(self):
          for node in self.nodelist_loop:
              yield node
          for node in self.nodelist_empty:
              yield node
  
      def render(self, context):
          if 'forloop' in context:
              parentloop = context['forloop']
          else:
              parentloop = {}
          context.push()
          try:
              values = self.sequence.resolve(context, True)
          except VariableDoesNotExist:
              values = []
          if values is None:
              values = []
          if not hasattr(values, '__len__'):
              values = list(values)
          len_values = len(values)
          if len_values < 1:
              context.pop()
              return self.nodelist_empty.render(context)
          nodelist = NodeList()
          if self.is_reversed:
              values = reversed(values)
          unpack = len(self.loopvars) > 1
          # Create a forloop value in the context.  We'll update counters on each
          # iteration just below.
          loop_dict = context['forloop'] = {'parentloop': parentloop}
          for i, item in enumerate(values):
              # Shortcuts for current loop iteration number.
              loop_dict['counter0'] = i
              loop_dict['counter'] = i+1
              # Reverse counter iteration numbers.
              loop_dict['revcounter'] = len_values - i
              loop_dict['revcounter0'] = len_values - i - 1
              # Boolean values designating first and last times through loop.
              loop_dict['first'] = (i == 0)
              loop_dict['last'] = (i == len_values - 1)
  
              pop_context = False
              if unpack:
                  # If there are multiple loop variables, unpack the item into
                  # them.
                  try:
                      unpacked_vars = dict(zip(self.loopvars, item))
                  except TypeError:
                      pass
                  else:
                      pop_context = True
                      context.update(unpacked_vars)
              else:
                  context[self.loopvars[0]] = item
              # In TEMPLATE_DEBUG mode provide source of the node which
              # actually raised the exception
              if settings.TEMPLATE_DEBUG:
                  for node in self.nodelist_loop:
                      try:
                          nodelist.append(node.render(context))
                      except Exception as e:
                          if not hasattr(e, 'django_template_source'):
                              e.django_template_source = node.source
                          raise
              else:
                  for node in self.nodelist_loop:
                      nodelist.append(node.render(context))
              if pop_context:
                  # The loop variables were pushed on to the context so pop them
                  # off again. This is necessary because the tag lets the length
                  # of loopvars differ to the length of each set of items and we
                  # don't want to leave any vars from the previous loop on the
                  # context.
                  context.pop()
          context.pop()
          return nodelist.render(context)
  
  class IfChangedNode(Node):
      child_nodelists = ('nodelist_true', 'nodelist_false')
  
      def __init__(self, nodelist_true, nodelist_false, *varlist):
          self.nodelist_true, self.nodelist_false = nodelist_true, nodelist_false
          self._last_seen = None
          self._varlist = varlist
          self._id = str(id(self))
  
      def render(self, context):
          if 'forloop' in context and self._id not in context['forloop']:
              self._last_seen = None
              context['forloop'][self._id] = 1
          try:
              if self._varlist:
                  # Consider multiple parameters.  This automatically behaves
                  # like an OR evaluation of the multiple variables.
                  compare_to = [var.resolve(context, True) for var in self._varlist]
              else:
                  compare_to = self.nodelist_true.render(context)
          except VariableDoesNotExist:
              compare_to = None
  
          if compare_to != self._last_seen:
              self._last_seen = compare_to
              content = self.nodelist_true.render(context)
              return content
          elif self.nodelist_false:
              return self.nodelist_false.render(context)
          return ''
  
  class IfEqualNode(Node):
      child_nodelists = ('nodelist_true', 'nodelist_false')
  
      def __init__(self, var1, var2, nodelist_true, nodelist_false, negate):
          self.var1, self.var2 = var1, var2
          self.nodelist_true, self.nodelist_false = nodelist_true, nodelist_false
          self.negate = negate
  
      def __repr__(self):
          return "<IfEqualNode>"
  
      def render(self, context):
          val1 = self.var1.resolve(context, True)
          val2 = self.var2.resolve(context, True)
          if (self.negate and val1 != val2) or (not self.negate and val1 == val2):
              return self.nodelist_true.render(context)
          return self.nodelist_false.render(context)
  
  class IfNode(Node):
  
      def __init__(self, conditions_nodelists):
          self.conditions_nodelists = conditions_nodelists
  
      def __repr__(self):
          return "<IfNode>"
  
      def __iter__(self):
          for _, nodelist in self.conditions_nodelists:
              for node in nodelist:
                  yield node
  
      @property
      def nodelist(self):
          return NodeList(node for _, nodelist in self.conditions_nodelists for node in nodelist)
  
      def render(self, context):
          for condition, nodelist in self.conditions_nodelists:
  
              if condition is not None:           # if / elif clause
                  try:
                      match = condition.eval(context)
                  except VariableDoesNotExist:
                      match = None
              else:                               # else clause
                  match = True
  
              if match:
                  return nodelist.render(context)
  
          return ''
  
  class RegroupNode(Node):
      def __init__(self, target, expression, var_name):
          self.target, self.expression = target, expression
          self.var_name = var_name
  
      def resolve_expression(self, obj, context):
          # This method is called for each object in self.target. See regroup()
          # for the reason why we temporarily put the object in the context.
          context[self.var_name] = obj
          return self.expression.resolve(context, True)
  
      def render(self, context):
          obj_list = self.target.resolve(context, True)
          if obj_list == None:
              # target variable wasn't found in context; fail silently.
              context[self.var_name] = []
              return ''
          # List of dictionaries in the format:
          # {'grouper': 'key', 'list': [list of contents]}.
          context[self.var_name] = [
              {'grouper': key, 'list': list(val)}
              for key, val in
              groupby(obj_list, lambda obj: self.resolve_expression(obj, context))
          ]
          return ''
  
  def include_is_allowed(filepath):
      for root in settings.ALLOWED_INCLUDE_ROOTS:
          if filepath.startswith(root):
              return True
      return False
  
  class SsiNode(Node):
      def __init__(self, filepath, parsed):
          self.filepath = filepath
          self.parsed = parsed
  
      def render(self, context):
          filepath = self.filepath.resolve(context)
  
          if not include_is_allowed(filepath):
              if settings.DEBUG:
                  return "[Didn't have permission to include file]"
              else:
                  return '' # Fail silently for invalid includes.
          try:
              fp = open(filepath, 'r')
              output = fp.read()
              fp.close()
          except IOError:
              output = ''
          if self.parsed:
              try:
                  t = Template(output, name=filepath)
                  return t.render(context)
              except TemplateSyntaxError as e:
                  if settings.DEBUG:
                      return "[Included template had syntax error: %s]" % e
                  else:
                      return '' # Fail silently for invalid included templates.
          return output
  
  class LoadNode(Node):
      def render(self, context):
          return ''
  
  class NowNode(Node):
      def __init__(self, format_string):
          self.format_string = format_string
  
      def render(self, context):
          tzinfo = timezone.get_current_timezone() if settings.USE_TZ else None
          return date(datetime.now(tz=tzinfo), self.format_string)
  
  class SpacelessNode(Node):
      def __init__(self, nodelist):
          self.nodelist = nodelist
  
      def render(self, context):
          from django.utils.html import strip_spaces_between_tags
          return strip_spaces_between_tags(self.nodelist.render(context).strip())
  
  class TemplateTagNode(Node):
      mapping = {'openblock': BLOCK_TAG_START,
                 'closeblock': BLOCK_TAG_END,
                 'openvariable': VARIABLE_TAG_START,
                 'closevariable': VARIABLE_TAG_END,
                 'openbrace': SINGLE_BRACE_START,
                 'closebrace': SINGLE_BRACE_END,
                 'opencomment': COMMENT_TAG_START,
                 'closecomment': COMMENT_TAG_END,
                 }
  
      def __init__(self, tagtype):
          self.tagtype = tagtype
  
      def render(self, context):
          return self.mapping.get(self.tagtype, '')
  
  class URLNode(Node):
      def __init__(self, view_name, args, kwargs, asvar):
          self.view_name = view_name
          self.args = args
          self.kwargs = kwargs
          self.asvar = asvar
  
      def render(self, context):
          from django.core.urlresolvers import reverse, NoReverseMatch
          args = [arg.resolve(context) for arg in self.args]
          kwargs = dict([(smart_str(k, 'ascii'), v.resolve(context))
                         for k, v in self.kwargs.items()])
  
          view_name = self.view_name.resolve(context)
  
          # Try to look up the URL twice: once given the view name, and again
          # relative to what we guess is the "main" app. If they both fail,
          # re-raise the NoReverseMatch unless we're using the
          # {% url ... as var %} construct in which cause return nothing.
          url = ''
          try:
              url = reverse(view_name, args=args, kwargs=kwargs, current_app=context.current_app)
          except NoReverseMatch as e:
              if settings.SETTINGS_MODULE:
                  project_name = settings.SETTINGS_MODULE.split('.')[0]
                  try:
                      url = reverse(project_name + '.' + view_name,
                                args=args, kwargs=kwargs,
                                current_app=context.current_app)
                  except NoReverseMatch:
                      if self.asvar is None:
                          # Re-raise the original exception, not the one with
                          # the path relative to the project. This makes a
                          # better error message.
                          raise e
              else:
                  if self.asvar is None:
                      raise e
  
          if self.asvar:
              context[self.asvar] = url
              return ''
          else:
              return url
  
  class WidthRatioNode(Node):
      def __init__(self, val_expr, max_expr, max_width):
          self.val_expr = val_expr
          self.max_expr = max_expr
          self.max_width = max_width
  
      def render(self, context):
          try:
              value = self.val_expr.resolve(context)
              max_value = self.max_expr.resolve(context)
              max_width = int(self.max_width.resolve(context))
          except VariableDoesNotExist:
              return ''
          except ValueError:
              raise TemplateSyntaxError("widthratio final argument must be an number")
          try:
              value = float(value)
              max_value = float(max_value)
              ratio = (value / max_value) * max_width
          except ZeroDivisionError:
              return '0'
          except ValueError:
              return ''
          return str(int(round(ratio)))
  
  class WithNode(Node):
      def __init__(self, var, name, nodelist, extra_context=None):
          self.nodelist = nodelist
          # var and name are legacy attributes, being left in case they are used
          # by third-party subclasses of this Node.
          self.extra_context = extra_context or {}
          if name:
              self.extra_context[name] = var
  
      def __repr__(self):
          return "<WithNode>"
  
      def render(self, context):
          values = dict([(key, val.resolve(context)) for key, val in
                         self.extra_context.iteritems()])
          context.update(values)
          output = self.nodelist.render(context)
          context.pop()
          return output
  
  @register.tag
  def autoescape(parser, token):
      """
      Force autoescape behavior for this block.
      """
      args = token.contents.split()
      if len(args) != 2:
          raise TemplateSyntaxError("'autoescape' tag requires exactly one argument.")
      arg = args[1]
      if arg not in (u'on', u'off'):
          raise TemplateSyntaxError("'autoescape' argument should be 'on' or 'off'")
      nodelist = parser.parse(('endautoescape',))
      parser.delete_first_token()
      return AutoEscapeControlNode((arg == 'on'), nodelist)
  
  @register.tag
  def comment(parser, token):
      """
      Ignores everything between ``{% comment %}`` and ``{% endcomment %}``.
      """
      parser.skip_past('endcomment')
      return CommentNode()
  
  @register.tag
  def cycle(parser, token):
      """
      Cycles among the given strings each time this tag is encountered.
  
      Within a loop, cycles among the given strings each time through
      the loop::
  
          {% for o in some_list %}
              <tr class="{% cycle 'row1' 'row2' %}">
                  ...
              </tr>
          {% endfor %}
  
      Outside of a loop, give the values a unique name the first time you call
      it, then use that name each sucessive time through::
  
              <tr class="{% cycle 'row1' 'row2' 'row3' as rowcolors %}">...</tr>
              <tr class="{% cycle rowcolors %}">...</tr>
              <tr class="{% cycle rowcolors %}">...</tr>
  
      You can use any number of values, separated by spaces. Commas can also
      be used to separate values; if a comma is used, the cycle values are
      interpreted as literal strings.
  
      The optional flag "silent" can be used to prevent the cycle declaration
      from returning any value::
  
          {% cycle 'row1' 'row2' as rowcolors silent %}{# no value here #}
          {% for o in some_list %}
              <tr class="{% cycle rowcolors %}">{# first value will be "row1" #}
                  ...
              </tr>
          {% endfor %}
  
      """
  
      # Note: This returns the exact same node on each {% cycle name %} call;
      # that is, the node object returned from {% cycle a b c as name %} and the
      # one returned from {% cycle name %} are the exact same object. This
      # shouldn't cause problems (heh), but if it does, now you know.
      #
      # Ugly hack warning: This stuffs the named template dict into parser so
      # that names are only unique within each template (as opposed to using
      # a global variable, which would make cycle names have to be unique across
      # *all* templates.
  
      args = token.split_contents()
  
      if len(args) < 2:
          raise TemplateSyntaxError("'cycle' tag requires at least two arguments")
  
      if ',' in args[1]:
          # Backwards compatibility: {% cycle a,b %} or {% cycle a,b as foo %}
          # case.
          args[1:2] = ['"%s"' % arg for arg in args[1].split(",")]
  
      if len(args) == 2:
          # {% cycle foo %} case.
          name = args[1]
          if not hasattr(parser, '_namedCycleNodes'):
              raise TemplateSyntaxError("No named cycles in template. '%s' is not defined" % name)
          if not name in parser._namedCycleNodes:
              raise TemplateSyntaxError("Named cycle '%s' does not exist" % name)
          return parser._namedCycleNodes[name]
  
      as_form = False
  
      if len(args) > 4:
          # {% cycle ... as foo [silent] %} case.
          if args[-3] == "as":
              if args[-1] != "silent":
                  raise TemplateSyntaxError("Only 'silent' flag is allowed after cycle's name, not '%s'." % args[-1])
              as_form = True
              silent = True
              args = args[:-1]
          elif args[-2] == "as":
              as_form = True
              silent = False
  
      if as_form:
          name = args[-1]
          values = [parser.compile_filter(arg) for arg in args[1:-2]]
          node = CycleNode(values, name, silent=silent)
          if not hasattr(parser, '_namedCycleNodes'):
              parser._namedCycleNodes = {}
          parser._namedCycleNodes[name] = node
      else:
          values = [parser.compile_filter(arg) for arg in args[1:]]
          node = CycleNode(values)
      return node
  
  @register.tag
  def csrf_token(parser, token):
      return CsrfTokenNode()
  
  @register.tag
  def debug(parser, token):
      """
      Outputs a whole load of debugging information, including the current
      context and imported modules.
  
      Sample usage::
  
          <pre>
              {% debug %}
          </pre>
      """
      return DebugNode()
  
  @register.tag('filter')
  def do_filter(parser, token):
      """
      Filters the contents of the block through variable filters.
  
      Filters can also be piped through each other, and they can have
      arguments -- just like in variable syntax.
  
      Sample usage::
  
          {% filter force_escape|lower %}
              This text will be HTML-escaped, and will appear in lowercase.
          {% endfilter %}
  
      Note that the ``escape`` and ``safe`` filters are not acceptable arguments.
      Instead, use the ``autoescape`` tag to manage autoescaping for blocks of
      template code.
      """
      _, rest = token.contents.split(None, 1)
      filter_expr = parser.compile_filter("var|%s" % (rest))
      for func, unused in filter_expr.filters:
          if getattr(func, '_decorated_function', func).__name__ in ('escape', 'safe'):
              raise TemplateSyntaxError('"filter %s" is not permitted.  Use the "autoescape" tag instead.' % func.__name__)
      nodelist = parser.parse(('endfilter',))
      parser.delete_first_token()
      return FilterNode(filter_expr, nodelist)
  
  @register.tag
  def firstof(parser, token):
      """
      Outputs the first variable passed that is not False, without escaping.
  
      Outputs nothing if all the passed variables are False.
  
      Sample usage::
  
          {% firstof var1 var2 var3 %}
  
      This is equivalent to::
  
          {% if var1 %}
              {{ var1|safe }}
          {% else %}{% if var2 %}
              {{ var2|safe }}
          {% else %}{% if var3 %}
              {{ var3|safe }}
          {% endif %}{% endif %}{% endif %}
  
      but obviously much cleaner!
  
      You can also use a literal string as a fallback value in case all
      passed variables are False::
  
          {% firstof var1 var2 var3 "fallback value" %}
  
      If you want to escape the output, use a filter tag::
  
          {% filter force_escape %}
              {% firstof var1 var2 var3 "fallback value" %}
          {% endfilter %}
  
      """
      bits = token.split_contents()[1:]
      if len(bits) < 1:
          raise TemplateSyntaxError("'firstof' statement requires at least one argument")
      return FirstOfNode([parser.compile_filter(bit) for bit in bits])
  
  @register.tag('for')
  def do_for(parser, token):
      """
      Loops over each item in an array.
  
      For example, to display a list of athletes given ``athlete_list``::
  
          <ul>
          {% for athlete in athlete_list %}
              <li>{{ athlete.name }}</li>
          {% endfor %}
          </ul>
  
      You can loop over a list in reverse by using
      ``{% for obj in list reversed %}``.
  
      You can also unpack multiple values from a two-dimensional array::
  
          {% for key,value in dict.items %}
              {{ key }}: {{ value }}
          {% endfor %}
  
      The ``for`` tag can take an optional ``{% empty %}`` clause that will
      be displayed if the given array is empty or could not be found::
  
          <ul>
            {% for athlete in athlete_list %}
              <li>{{ athlete.name }}</li>
            {% empty %}
              <li>Sorry, no athletes in this list.</li>
            {% endfor %}
          <ul>
  
      The above is equivalent to -- but shorter, cleaner, and possibly faster
      than -- the following::
  
          <ul>
            {% if althete_list %}
              {% for athlete in athlete_list %}
                <li>{{ athlete.name }}</li>
              {% endfor %}
            {% else %}
              <li>Sorry, no athletes in this list.</li>
            {% endif %}
          </ul>
  
      The for loop sets a number of variables available within the loop:
  
          ==========================  ================================================
          Variable                    Description
          ==========================  ================================================
          ``forloop.counter``         The current iteration of the loop (1-indexed)
          ``forloop.counter0``        The current iteration of the loop (0-indexed)
          ``forloop.revcounter``      The number of iterations from the end of the
                                      loop (1-indexed)
          ``forloop.revcounter0``     The number of iterations from the end of the
                                      loop (0-indexed)
          ``forloop.first``           True if this is the first time through the loop
          ``forloop.last``            True if this is the last time through the loop
          ``forloop.parentloop``      For nested loops, this is the loop "above" the
                                      current one
          ==========================  ================================================
  
      """
      bits = token.contents.split()
      if len(bits) < 4:
          raise TemplateSyntaxError("'for' statements should have at least four"
                                    " words: %s" % token.contents)
  
      is_reversed = bits[-1] == 'reversed'
      in_index = is_reversed and -3 or -2
      if bits[in_index] != 'in':
          raise TemplateSyntaxError("'for' statements should use the format"
                                    " 'for x in y': %s" % token.contents)
  
      loopvars = re.split(r' *, *', ' '.join(bits[1:in_index]))
      for var in loopvars:
          if not var or ' ' in var:
              raise TemplateSyntaxError("'for' tag received an invalid argument:"
                                        " %s" % token.contents)
  
      sequence = parser.compile_filter(bits[in_index+1])
      nodelist_loop = parser.parse(('empty', 'endfor',))
      token = parser.next_token()
      if token.contents == 'empty':
          nodelist_empty = parser.parse(('endfor',))
          parser.delete_first_token()
      else:
          nodelist_empty = None
      return ForNode(loopvars, sequence, is_reversed, nodelist_loop, nodelist_empty)
  
  def do_ifequal(parser, token, negate):
      bits = list(token.split_contents())
      if len(bits) != 3:
          raise TemplateSyntaxError("%r takes two arguments" % bits[0])
      end_tag = 'end' + bits[0]
      nodelist_true = parser.parse(('else', end_tag))
      token = parser.next_token()
      if token.contents == 'else':
          nodelist_false = parser.parse((end_tag,))
          parser.delete_first_token()
      else:
          nodelist_false = NodeList()
      val1 = parser.compile_filter(bits[1])
      val2 = parser.compile_filter(bits[2])
      return IfEqualNode(val1, val2, nodelist_true, nodelist_false, negate)
  
  @register.tag
  def ifequal(parser, token):
      """
      Outputs the contents of the block if the two arguments equal each other.
  
      Examples::
  
          {% ifequal user.id comment.user_id %}
              ...
          {% endifequal %}
  
          {% ifnotequal user.id comment.user_id %}
              ...
          {% else %}
              ...
          {% endifnotequal %}
      """
      return do_ifequal(parser, token, False)
  
  @register.tag
  def ifnotequal(parser, token):
      """
      Outputs the contents of the block if the two arguments are not equal.
      See ifequal.
      """
      return do_ifequal(parser, token, True)
  
  class TemplateLiteral(Literal):
      def __init__(self, value, text):
          self.value = value
          self.text = text # for better error messages
  
      def display(self):
          return self.text
  
      def eval(self, context):
          return self.value.resolve(context, ignore_failures=True)
  
  class TemplateIfParser(IfParser):
      error_class = TemplateSyntaxError
  
      def __init__(self, parser, *args, **kwargs):
          self.template_parser = parser
          super(TemplateIfParser, self).__init__(*args, **kwargs)
  
      def create_var(self, value):
          return TemplateLiteral(self.template_parser.compile_filter(value), value)
  
  @register.tag('if')
  def do_if(parser, token):
      """
      The ``{% if %}`` tag evaluates a variable, and if that variable is "true"
      (i.e., exists, is not empty, and is not a false boolean value), the
      contents of the block are output:
  
      ::
  
          {% if athlete_list %}
              Number of athletes: {{ athlete_list|count }}
          {% elif athlete_in_locker_room_list %}
              Athletes should be out of the locker room soon!
          {% else %}
              No athletes.
          {% endif %}
  
      In the above, if ``athlete_list`` is not empty, the number of athletes will
      be displayed by the ``{{ athlete_list|count }}`` variable.
  
      As you can see, the ``if`` tag may take one or several `` {% elif %}``
      clauses, as well as an ``{% else %}`` clause that will be displayed if all
      previous conditions fail. These clauses are optional.
  
      ``if`` tags may use ``or``, ``and`` or ``not`` to test a number of
      variables or to negate a given variable::
  
          {% if not athlete_list %}
              There are no athletes.
          {% endif %}
  
          {% if athlete_list or coach_list %}
              There are some athletes or some coaches.
          {% endif %}
  
          {% if athlete_list and coach_list %}
              Both atheletes and coaches are available.
          {% endif %}
  
          {% if not athlete_list or coach_list %}
              There are no athletes, or there are some coaches.
          {% endif %}
  
          {% if athlete_list and not coach_list %}
              There are some athletes and absolutely no coaches.
          {% endif %}
  
      Comparison operators are also available, and the use of filters is also
      allowed, for example::
  
          {% if articles|length >= 5 %}...{% endif %}
  
      Arguments and operators _must_ have a space between them, so
      ``{% if 1>2 %}`` is not a valid if tag.
  
      All supported operators are: ``or``, ``and``, ``in``, ``not in``
      ``==`` (or ``=``), ``!=``, ``>``, ``>=``, ``<`` and ``<=``.
  
      Operator precedence follows Python.
      """
      # {% if ... %}
      bits = token.split_contents()[1:]
      condition = TemplateIfParser(parser, bits).parse()
      nodelist = parser.parse(('elif', 'else', 'endif'))
      conditions_nodelists = [(condition, nodelist)]
      token = parser.next_token()
  
      # {% elif ... %} (repeatable)
      while token.contents.startswith('elif'):
          bits = token.split_contents()[1:]
          condition = TemplateIfParser(parser, bits).parse()
          nodelist = parser.parse(('elif', 'else', 'endif'))
          conditions_nodelists.append((condition, nodelist))
          token = parser.next_token()
  
      # {% else %} (optional)
      if token.contents == 'else':
          nodelist = parser.parse(('endif',))
          conditions_nodelists.append((None, nodelist))
          token = parser.next_token()
  
      # {% endif %}
      assert token.contents == 'endif'
  
      return IfNode(conditions_nodelists)
  
  
  @register.tag
  def ifchanged(parser, token):
      """
      Checks if a value has changed from the last iteration of a loop.
  
      The ``{% ifchanged %}`` block tag is used within a loop. It has two
      possible uses.
  
      1. Checks its own rendered contents against its previous state and only
         displays the content if it has changed. For example, this displays a
         list of days, only displaying the month if it changes::
  
              <h1>Archive for {{ year }}</h1>
  
              {% for date in days %}
                  {% ifchanged %}<h3>{{ date|date:"F" }}</h3>{% endifchanged %}
                  <a href="{{ date|date:"M/d"|lower }}/">{{ date|date:"j" }}</a>
              {% endfor %}
  
      2. If given one or more variables, check whether any variable has changed.
         For example, the following shows the date every time it changes, while
         showing the hour if either the hour or the date has changed::
  
              {% for date in days %}
                  {% ifchanged date.date %} {{ date.date }} {% endifchanged %}
                  {% ifchanged date.hour date.date %}
                      {{ date.hour }}
                  {% endifchanged %}
              {% endfor %}
      """
      bits = token.contents.split()
      nodelist_true = parser.parse(('else', 'endifchanged'))
      token = parser.next_token()
      if token.contents == 'else':
          nodelist_false = parser.parse(('endifchanged',))
          parser.delete_first_token()
      else:
          nodelist_false = NodeList()
      values = [parser.compile_filter(bit) for bit in bits[1:]]
      return IfChangedNode(nodelist_true, nodelist_false, *values)
  
  @register.tag
  def ssi(parser, token):
      """
      Outputs the contents of a given file into the page.
  
      Like a simple "include" tag, the ``ssi`` tag includes the contents
      of another file -- which must be specified using an absolute path --
      in the current page::
  
          {% ssi "/home/html/ljworld.com/includes/right_generic.html" %}
  
      If the optional "parsed" parameter is given, the contents of the included
      file are evaluated as template code, with the current context::
  
          {% ssi "/home/html/ljworld.com/includes/right_generic.html" parsed %}
      """
      bits = token.split_contents()
      parsed = False
      if len(bits) not in (2, 3):
          raise TemplateSyntaxError("'ssi' tag takes one argument: the path to"
                                    " the file to be included")
      if len(bits) == 3:
          if bits[2] == 'parsed':
              parsed = True
          else:
              raise TemplateSyntaxError("Second (optional) argument to %s tag"
                                        " must be 'parsed'" % bits[0])
      filepath = parser.compile_filter(bits[1])
      return SsiNode(filepath, parsed)
  
  @register.tag
  def load(parser, token):
      """
      Loads a custom template tag set.
  
      For example, to load the template tags in
      ``django/templatetags/news/photos.py``::
  
          {% load news.photos %}
  
      Can also be used to load an individual tag/filter from
      a library::
  
          {% load byline from news %}
  
      """
      bits = token.contents.split()
      if len(bits) >= 4 and bits[-2] == "from":
          try:
              taglib = bits[-1]
              lib = get_library(taglib)
          except InvalidTemplateLibrary as e:
              raise TemplateSyntaxError("'%s' is not a valid tag library: %s" %
                                        (taglib, e))
          else:
              temp_lib = Library()
              for name in bits[1:-2]:
                  if name in lib.tags:
                      temp_lib.tags[name] = lib.tags[name]
                      # a name could be a tag *and* a filter, so check for both
                      if name in lib.filters:
                          temp_lib.filters[name] = lib.filters[name]
                  elif name in lib.filters:
                      temp_lib.filters[name] = lib.filters[name]
                  else:
                      raise TemplateSyntaxError("'%s' is not a valid tag or filter in tag library '%s'" %
                                                (name, taglib))
              parser.add_library(temp_lib)
      else:
          for taglib in bits[1:]:
              # add the library to the parser
              try:
                  lib = get_library(taglib)
                  parser.add_library(lib)
              except InvalidTemplateLibrary as e:
                  raise TemplateSyntaxError("'%s' is not a valid tag library: %s" %
                                            (taglib, e))
      return LoadNode()
  
  @register.tag
  def now(parser, token):
      """
      Displays the date, formatted according to the given string.
  
      Uses the same format as PHP's ``date()`` function; see http://php.net/date
      for all the possible values.
  
      Sample usage::
  
          It is {% now "jS F Y H:i" %}
      """
      bits = token.split_contents()
      if len(bits) != 2:
          raise TemplateSyntaxError("'now' statement takes one argument")
      format_string = bits[1][1:-1]
      return NowNode(format_string)
  
  @register.tag
  def regroup(parser, token):
      """
      Regroups a list of alike objects by a common attribute.
  
      This complex tag is best illustrated by use of an example:  say that
      ``people`` is a list of ``Person`` objects that have ``first_name``,
      ``last_name``, and ``gender`` attributes, and you'd like to display a list
      that looks like:
  
          * Male:
              * George Bush
              * Bill Clinton
          * Female:
              * Margaret Thatcher
              * Colendeeza Rice
          * Unknown:
              * Pat Smith
  
      The following snippet of template code would accomplish this dubious task::
  
          {% regroup people by gender as grouped %}
          <ul>
          {% for group in grouped %}
              <li>{{ group.grouper }}
              <ul>
                  {% for item in group.list %}
                  <li>{{ item }}</li>
                  {% endfor %}
              </ul>
          {% endfor %}
          </ul>
  
      As you can see, ``{% regroup %}`` populates a variable with a list of
      objects with ``grouper`` and ``list`` attributes.  ``grouper`` contains the
      item that was grouped by; ``list`` contains the list of objects that share
      that ``grouper``.  In this case, ``grouper`` would be ``Male``, ``Female``
      and ``Unknown``, and ``list`` is the list of people with those genders.
  
      Note that ``{% regroup %}`` does not work when the list to be grouped is not
      sorted by the key you are grouping by!  This means that if your list of
      people was not sorted by gender, you'd need to make sure it is sorted
      before using it, i.e.::
  
          {% regroup people|dictsort:"gender" by gender as grouped %}
  
      """
      firstbits = token.contents.split(None, 3)
      if len(firstbits) != 4:
          raise TemplateSyntaxError("'regroup' tag takes five arguments")
      target = parser.compile_filter(firstbits[1])
      if firstbits[2] != 'by':
          raise TemplateSyntaxError("second argument to 'regroup' tag must be 'by'")
      lastbits_reversed = firstbits[3][::-1].split(None, 2)
      if lastbits_reversed[1][::-1] != 'as':
          raise TemplateSyntaxError("next-to-last argument to 'regroup' tag must"
                                    " be 'as'")
      var_name = lastbits_reversed[0][::-1]
      # RegroupNode will take each item in 'target', put it in the context under
      # 'var_name', evaluate 'var_name'.'expression' in the current context, and
      # group by the resulting value. After all items are processed, it will
      # save the final result in the context under 'var_name', thus clearing the
      # temporary values. This hack is necessary because the template engine
      # doesn't provide a context-aware equivalent of Python's getattr.
      expression = parser.compile_filter(var_name +
                                         VARIABLE_ATTRIBUTE_SEPARATOR +
                                         lastbits_reversed[2][::-1])
      return RegroupNode(target, expression, var_name)
  
  @register.tag
  def spaceless(parser, token):
      """
      Removes whitespace between HTML tags, including tab and newline characters.
  
      Example usage::
  
          {% spaceless %}
              <p>
                  <a href="foo/">Foo</a>
              </p>
          {% endspaceless %}
  
      This example would return this HTML::
  
          <p><a href="foo/">Foo</a></p>
  
      Only space between *tags* is normalized -- not space between tags and text.
      In this example, the space around ``Hello`` won't be stripped::
  
          {% spaceless %}
              <strong>
                  Hello
              </strong>
          {% endspaceless %}
      """
      nodelist = parser.parse(('endspaceless',))
      parser.delete_first_token()
      return SpacelessNode(nodelist)
  
  @register.tag
  def templatetag(parser, token):
      """
      Outputs one of the bits used to compose template tags.
  
      Since the template system has no concept of "escaping", to display one of
      the bits used in template tags, you must use the ``{% templatetag %}`` tag.
  
      The argument tells which template bit to output:
  
          ==================  =======
          Argument            Outputs
          ==================  =======
          ``openblock``       ``{%``
          ``closeblock``      ``%}``
          ``openvariable``    ``{{``
          ``closevariable``   ``}}``
          ``openbrace``       ``{``
          ``closebrace``      ``}``
          ``opencomment``     ``{#``
          ``closecomment``    ``#}``
          ==================  =======
      """
      bits = token.contents.split()
      if len(bits) != 2:
          raise TemplateSyntaxError("'templatetag' statement takes one argument")
      tag = bits[1]
      if tag not in TemplateTagNode.mapping:
          raise TemplateSyntaxError("Invalid templatetag argument: '%s'."
                                    " Must be one of: %s" %
                                    (tag, TemplateTagNode.mapping.keys()))
      return TemplateTagNode(tag)
  
  @register.tag
  def url(parser, token):
      """
      Returns an absolute URL matching given view with its parameters.
  
      This is a way to define links that aren't tied to a particular URL
      configuration::
  
          {% url "path.to.some_view" arg1 arg2 %}
  
          or
  
          {% url "path.to.some_view" name1=value1 name2=value2 %}
  
      The first argument is a path to a view. It can be an absolute Python path
      or just ``app_name.view_name`` without the project name if the view is
      located inside the project.
  
      Other arguments are space-separated values that will be filled in place of
      positional and keyword arguments in the URL. Don't mix positional and
      keyword arguments.
  
      All arguments for the URL should be present.
  
      For example if you have a view ``app_name.client`` taking client's id and
      the corresponding line in a URLconf looks like this::
  
          ('^client/(\d+)/$', 'app_name.client')
  
      and this app's URLconf is included into the project's URLconf under some
      path::
  
          ('^clients/', include('project_name.app_name.urls'))
  
      then in a template you can create a link for a certain client like this::
  
          {% url "app_name.client" client.id %}
  
      The URL will look like ``/clients/client/123/``.
  
      The first argument can also be a named URL instead of the Python path to
      the view callable. For example if the URLconf entry looks like this::
  
          url('^client/(\d+)/$', name='client-detail-view')
  
      then in the template you can use::
  
          {% url "client-detail-view" client.id %}
  
      There is even another possible value type for the first argument. It can be
      the name of a template variable that will be evaluated to obtain the view
      name or the URL name, e.g.::
  
          {% with view_path="app_name.client" %}
          {% url view_path client.id %}
          {% endwith %}
  
          or,
  
          {% with url_name="client-detail-view" %}
          {% url url_name client.id %}
          {% endwith %}
  
      """
      bits = token.split_contents()
      if len(bits) < 2:
          raise TemplateSyntaxError("'%s' takes at least one argument"
                                    " (path to a view)" % bits[0])
      viewname = parser.compile_filter(bits[1])
      args = []
      kwargs = {}
      asvar = None
      bits = bits[2:]
      if len(bits) >= 2 and bits[-2] == 'as':
          asvar = bits[-1]
          bits = bits[:-2]
  
      if len(bits):
          for bit in bits:
              match = kwarg_re.match(bit)
              if not match:
                  raise TemplateSyntaxError("Malformed arguments to url tag")
              name, value = match.groups()
              if name:
                  kwargs[name] = parser.compile_filter(value)
              else:
                  args.append(parser.compile_filter(value))
  
      return URLNode(viewname, args, kwargs, asvar)
  
  @register.tag
  def widthratio(parser, token):
      """
      For creating bar charts and such, this tag calculates the ratio of a given
      value to a maximum value, and then applies that ratio to a constant.
  
      For example::
  
          <img src='bar.gif' height='10' width='{% widthratio this_value max_value 100 %}' />
  
      Above, if ``this_value`` is 175 and ``max_value`` is 200, the image in
      the above example will be 88 pixels wide (because 175/200 = .875;
      .875 * 100 = 87.5 which is rounded up to 88).
      """
      bits = token.contents.split()
      if len(bits) != 4:
          raise TemplateSyntaxError("widthratio takes three arguments")
      tag, this_value_expr, max_value_expr, max_width = bits
  
      return WidthRatioNode(parser.compile_filter(this_value_expr),
                            parser.compile_filter(max_value_expr),
                            parser.compile_filter(max_width))
  
  @register.tag('with')
  def do_with(parser, token):
      """
      Adds one or more values to the context (inside of this block) for caching
      and easy access.
  
      For example::
  
          {% with total=person.some_sql_method %}
              {{ total }} object{{ total|pluralize }}
          {% endwith %}
  
      Multiple values can be added to the context::
  
          {% with foo=1 bar=2 %}
              ...
          {% endwith %}
  
      The legacy format of ``{% with person.some_sql_method as total %}`` is
      still accepted.
      """
      bits = token.split_contents()
      remaining_bits = bits[1:]
      extra_context = token_kwargs(remaining_bits, parser, support_legacy=True)
      if not extra_context:
          raise TemplateSyntaxError("%r expected at least one variable "
                                    "assignment" % bits[0])
      if remaining_bits:
          raise TemplateSyntaxError("%r received an invalid token: %r" %
                                    (bits[0], remaining_bits[0]))
      nodelist = parser.parse(('endwith',))
      parser.delete_first_token()
      return WithNode(None, None, nodelist, extra_context=extra_context)
  