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"""Default tags used by the template system, available to all templates."""
from __future__ import unicode_literals
import re
import sys
import warnings
from datetime import datetime
from itertools import cycle as itertools_cycle, groupby
from django.conf import settings
from django.utils import six, timezone
from django.utils.encoding import force_text, smart_text
from django.utils.html import conditional_escape, format_html
from django.utils.lorem_ipsum import paragraphs, words
from django.utils.safestring import mark_safe
from .base import (
TemplateSyntaxError, VariableDoesNotExist, kwarg_re,
render_value_in_context, token_kwargs,
from .defaultfilters import date
from .library import Library
from .smartif import IfParser, Literal
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)
return output
class CommentNode(Node):
def render(self, context):
return ''
class CsrfTokenNode(Node):
def render(self, context):
csrf_token = context.get('csrf_token')
if csrf_token:
if csrf_token == 'NOTPROVIDED':
return format_html("")
return format_html("<input type='hidden' name='csrfmiddlewaretoken' value='{}' />", csrf_token)
# It's very probable that the token is missing because of
# misconfiguration, so we raise a warning
if settings.DEBUG:
"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 ''
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 = next(cycle_iter).resolve(context)
if self.variable_name:
context[self.variable_name] = value
if self.silent:
return ''
return render_value_in_context(value, context)
class DebugNode(Node):
def render(self, context):
from pprint import pformat
output = [force_text(pformat(val)) for val in context]
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.
with context.push(var=output):
return self.filter_expr.resolve(context)
class FirstOfNode(Node):
def __init__(self, variables, asvar=None):
self.vars = variables
self.asvar = asvar
def render(self, context):
for var in self.vars:
value = var.resolve(context, True)
if value:
first = render_value_in_context(value, context)
if self.asvar:
context[self.asvar] = first
return ''
return first
return ''
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()
self.nodelist_empty = nodelist_empty
def __repr__(self):
reversed_text = ' reversed' if self.is_reversed else ''
return "<For Node: for %s in %s, tail_len: %d%s>" % \
(', '.join(self.loopvars), self.sequence, len(self.nodelist_loop),
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']
parentloop = {}
with context.push():
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:
return self.nodelist_empty.render(context)
nodelist = []
if self.is_reversed:
values = reversed(values)
num_loopvars = len(self.loopvars)
unpack = num_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.
# To complete this deprecation, remove from here to the
# try/except block as well as the try/except itself,
# leaving `unpacked_vars = ...` and the "else" statements.
if not isinstance(item, (list, tuple)):
len_item = 1
len_item = len(item)
# Check loop variable count before unpacking
if num_loopvars != len_item:
raise ValueError(
"Need {} values to unpack in for loop; got {}. "
.format(num_loopvars, len_item),
unpacked_vars = dict(zip(self.loopvars, item))
except TypeError:
pop_context = True
context[self.loopvars[0]] = item
for node in self.nodelist_loop:
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.
return mark_safe(''.join(force_text(n) for n in nodelist))
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._varlist = varlist
def render(self, context):
# Init state storage
state_frame = self._get_context_stack_frame(context)
if self not in state_frame:
state_frame[self] = None
nodelist_true_output = None
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]
# The "{% ifchanged %}" syntax (without any variables) compares the rendered output.
compare_to = nodelist_true_output = self.nodelist_true.render(context)
except VariableDoesNotExist:
compare_to = None
if compare_to != state_frame[self]:
state_frame[self] = compare_to
# render true block if not already rendered
return nodelist_true_output or self.nodelist_true.render(context)
elif self.nodelist_false:
return self.nodelist_false.render(context)
return ''
def _get_context_stack_frame(self, context):
# The Context object behaves like a stack where each template tag can create a new scope.
# Find the place where to store the state to detect changes.
if 'forloop' in context:
# Ifchanged is bound to the local for loop.
# When there is a loop-in-loop, the state is bound to the inner loop,
# so it resets when the outer loop continues.
return context['forloop']
# Using ifchanged outside loops. Effectively this is a no-op because the state is associated with 'self'.
return context.render_context
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
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
match = condition.eval(context)
except VariableDoesNotExist:
match = None
else: # else clause
match = True
if match:
return nodelist.render(context)
return ''
class LoremNode(Node):
def __init__(self, count, method, common):
self.count, self.method, self.common = count, method, common
def render(self, context):
count = int(self.count.resolve(context))
except (ValueError, TypeError):
count = 1
if self.method == 'w':
return words(count, common=self.common)
paras = paragraphs(count, common=self.common)
if self.method == 'p':
paras = ['<p>%s</p>' % p for p in paras]
return '\n\n'.join(paras)
class RegroupNode(Node):
def __init__(self, target, expression, var_name):, self.expression = target, expression
self.var_name = var_name
def resolve_expression(self, obj, context):
# This method is called for each object in 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 =, True)
if obj_list is 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 ''
class LoadNode(Node):
def render(self, context):
return ''
class NowNode(Node):
def __init__(self, format_string, asvar=None):
self.format_string = format_string
self.asvar = asvar
def render(self, context):
tzinfo = timezone.get_current_timezone() if settings.USE_TZ else None
formatted = date(, self.format_string)
if self.asvar:
context[self.asvar] = formatted
return ''
return formatted
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.urls import reverse, NoReverseMatch
args = [arg.resolve(context) for arg in self.args]
kwargs = {
smart_text(k, 'ascii'): v.resolve(context)
for k, v in self.kwargs.items()
view_name = self.view_name.resolve(context)
current_app = context.request.current_app
except AttributeError:
current_app = context.request.resolver_match.namespace
except AttributeError:
current_app = None
# Try to look up the URL. If it fails, raise NoReverseMatch unless the
# {% url ... as var %} construct is used, in which case return nothing.
url = ''
url = reverse(view_name, args=args, kwargs=kwargs, current_app=current_app)
except NoReverseMatch:
if self.asvar is None:
if self.asvar:
context[self.asvar] = url
return ''
if context.autoescape:
url = conditional_escape(url)
return url
class VerbatimNode(Node):
def __init__(self, content):
self.content = content
def render(self, context):
return self.content
class WidthRatioNode(Node):
def __init__(self, val_expr, max_expr, max_width, asvar=None):
self.val_expr = val_expr
self.max_expr = max_expr
self.max_width = max_width
self.asvar = asvar
def render(self, context):
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, TypeError):
raise TemplateSyntaxError("widthratio final argument must be a number")
value = float(value)
max_value = float(max_value)
ratio = (value / max_value) * max_width
result = str(int(round(ratio)))
except ZeroDivisionError:
return '0'
except (ValueError, TypeError, OverflowError):
return ''
if self.asvar:
context[self.asvar] = result
return ''
return result
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 = {key: val.resolve(context) for key, val in
with context.push(**values):
return self.nodelist.render(context)
def autoescape(parser, token):
Force autoescape behavior for this block.
# token.split_contents() isn't useful here because this tag doesn't accept variable as arguments
args = token.contents.split()
if len(args) != 2:
raise TemplateSyntaxError("'autoescape' tag requires exactly one argument.")
arg = args[1]
if arg not in ('on', 'off'):
raise TemplateSyntaxError("'autoescape' argument should be 'on' or 'off'")
nodelist = parser.parse(('endautoescape',))
return AutoEscapeControlNode((arg == 'on'), nodelist)
def comment(parser, token):
Ignores everything between ``{% comment %}`` and ``{% endcomment %}``.
return CommentNode()
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' %}">
{% endfor %}
Outside of a loop, give the values a unique name the first time you call
it, then use that name each successive 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::
{% for o in some_list %}
{% cycle 'row1' 'row2' as rowcolors silent %}
<tr class="{{ rowcolors }}">{% include "subtemplate.html " %}</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 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 name not 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
values = [parser.compile_filter(arg) for arg in args[1:]]
node = CycleNode(values)
return node
def csrf_token(parser, token):
return CsrfTokenNode()
def debug(parser, token):
Outputs a whole load of debugging information, including the current
context and imported modules.
Sample usage::
{% debug %}
return DebugNode()
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.
# token.split_contents() isn't useful here because this tag doesn't accept variable as arguments
_, rest = token.contents.split(None, 1)
filter_expr = parser.compile_filter("var|%s" % (rest))
for func, unused in filter_expr.filters:
filter_name = getattr(func, '_filter_name', None)
if filter_name in ('escape', 'safe'):
raise TemplateSyntaxError('"filter %s" is not permitted. Use the "autoescape" tag instead.' % filter_name)
nodelist = parser.parse(('endfilter',))
return FilterNode(filter_expr, nodelist)
def firstof(parser, token):
Outputs the first variable passed that is not False.
Outputs nothing if all the passed variables are False.
Sample usage::
{% firstof var1 var2 var3 as myvar %}
This is equivalent to::
{% if var1 %}
{{ var1 }}
{% elif var2 %}
{{ var2 }}
{% elif var3 %}
{{ var3 }}
{% 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 disable auto-escaping of variables you can use::
{% autoescape off %}
{% firstof var1 var2 var3 "<strong>fallback value</strong>" %}
{% autoescape %}
Or if only some variables should be escaped, you can use::
{% firstof var1 var2|safe var3 "<strong>fallback value</strong>"|safe %}
bits = token.split_contents()[1:]
asvar = None
if len(bits) < 1:
raise TemplateSyntaxError("'firstof' statement requires at least one argument")
if len(bits) >= 2 and bits[-2] == 'as':
asvar = bits[-1]
bits = bits[:-2]
return FirstOfNode([parser.compile_filter(bit) for bit in bits], asvar)
def do_for(parser, token):
Loops over each item in an array.
For example, to display a list of athletes given ``athlete_list``::
{% for athlete in athlete_list %}
<li>{{ }}</li>
{% endfor %}
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::
{% for athlete in athlete_list %}
<li>{{ }}</li>
{% empty %}
<li>Sorry, no athletes in this list.</li>
{% endfor %}
The above is equivalent to -- but shorter, cleaner, and possibly faster
than -- the following::
{% if athlete_list %}
{% for athlete in athlete_list %}
<li>{{ }}</li>
{% endfor %}
{% else %}
<li>Sorry, no athletes in this list.</li>
{% endif %}
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.split_contents()
if len(bits) < 4:
raise TemplateSyntaxError("'for' statements should have at least four"
" words: %s" % token.contents)
is_reversed = bits[-1] == 'reversed'
in_index = -3 if is_reversed else -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',))
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,))
nodelist_false = NodeList()
val1 = parser.compile_filter(bits[1])
val2 = parser.compile_filter(bits[2])
return IfEqualNode(val1, val2, nodelist_true, nodelist_false, negate)
def ifequal(parser, token):
Outputs the contents of the block if the two arguments equal each other.
{% ifequal comment.user_id %}
{% endifequal %}
{% ifnotequal comment.user_id %}
{% else %}
{% endifnotequal %}
return do_ifequal(parser, token, False)
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)
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 athletes 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``
``==``, ``!=``, ``>``, ``>=``, ``<`` 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 %}
if token.contents != 'endif':
raise TemplateSyntaxError('Malformed template tag at line {0}: "{1}"'.format(token.lineno, token.contents))
return IfNode(conditions_nodelists)
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 %} {{ }} {% endifchanged %}
{% ifchanged date.hour %}
{{ date.hour }}
{% endifchanged %}
{% endfor %}
bits = token.split_contents()
nodelist_true = parser.parse(('else', 'endifchanged'))
token = parser.next_token()
if token.contents == 'else':
nodelist_false = parser.parse(('endifchanged',))
nodelist_false = NodeList()
values = [parser.compile_filter(bit) for bit in bits[1:]]
return IfChangedNode(nodelist_true, nodelist_false, *values)
def find_library(parser, name):
return parser.libraries[name]
except KeyError:
raise TemplateSyntaxError(
"'%s' is not a registered tag library. Must be one of:\n%s" % (
name, "\n".join(sorted(parser.libraries.keys())),
def load_from_library(library, label, names):
Return a subset of tags and filters from a library.
subset = Library()
for name in names:
found = False
if name in library.tags:
found = True
subset.tags[name] = library.tags[name]
if name in library.filters:
found = True
subset.filters[name] = library.filters[name]
if found is False:
raise TemplateSyntaxError(
"'%s' is not a valid tag or filter in tag library '%s'" % (
name, label,
return subset
def load(parser, token):
Loads a custom template tag library into the parser.
For example, to load the template tags in
{% load %}
Can also be used to load an individual tag/filter from
a library::
{% load byline from news %}
# token.split_contents() isn't useful here because this tag doesn't accept variable as arguments
bits = token.contents.split()
if len(bits) >= 4 and bits[-2] == "from":
# from syntax is used; load individual tags from the library
name = bits[-1]
lib = find_library(parser, name)
subset = load_from_library(lib, name, bits[1:-2])
# one or more libraries are specified; load and add them to the parser
for name in bits[1:]:
lib = find_library(parser, name)
return LoadNode()
def lorem(parser, token):
Creates random Latin text useful for providing test data in templates.
Usage format::
{% lorem [count] [method] [random] %}
``count`` is a number (or variable) containing the number of paragraphs or
words to generate (default is 1).
``method`` is either ``w`` for words, ``p`` for HTML paragraphs, ``b`` for
plain-text paragraph blocks (default is ``b``).
``random`` is the word ``random``, which if given, does not use the common
paragraph (starting "Lorem ipsum dolor sit amet, consectetuer...").
* ``{% lorem %}`` will output the common "lorem ipsum" paragraph
* ``{% lorem 3 p %}`` will output the common "lorem ipsum" paragraph
and two random paragraphs each wrapped in HTML ``<p>`` tags
* ``{% lorem 2 w random %}`` will output two random latin words
bits = list(token.split_contents())
tagname = bits[0]
# Random bit
common = bits[-1] != 'random'
if not common:
# Method bit
if bits[-1] in ('w', 'p', 'b'):
method = bits.pop()
method = 'b'
# Count bit
if len(bits) > 1:
count = bits.pop()
count = '1'
count = parser.compile_filter(count)
if len(bits) != 1:
raise TemplateSyntaxError("Incorrect format for %r tag" % tagname)
return LoremNode(count, method, common)
def now(parser, token):
Displays the date, formatted according to the given string.
Uses the same format as PHP's ``date()`` function; see
for all the possible values.
Sample usage::
It is {% now "jS F Y H:i" %}
bits = token.split_contents()
asvar = None
if len(bits) == 4 and bits[-2] == 'as':
asvar = bits[-1]
bits = bits[:-2]
if len(bits) != 2:
raise TemplateSyntaxError("'now' statement takes one argument")
format_string = bits[1][1:-1]
return NowNode(format_string, asvar)
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 %}
{% for group in grouped %}
<li>{{ group.grouper }}
{% for item in group.list %}
<li>{{ item }}</li>
{% endfor %}
{% endfor %}
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 %}
bits = token.split_contents()
if len(bits) != 6:
raise TemplateSyntaxError("'regroup' tag takes five arguments")
target = parser.compile_filter(bits[1])
if bits[2] != 'by':
raise TemplateSyntaxError("second argument to 'regroup' tag must be 'by'")
if bits[4] != 'as':
raise TemplateSyntaxError("next-to-last argument to 'regroup' tag must"
" be 'as'")
var_name = bits[5]
# 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 +
return RegroupNode(target, expression, var_name)
def spaceless(parser, token):
Removes whitespace between HTML tags, including tab and newline characters.
Example usage::
{% spaceless %}
<a href="foo/">Foo</a>
{% 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 %}
{% endspaceless %}
nodelist = parser.parse(('endspaceless',))
return SpacelessNode(nodelist)
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`` ``#}``
================== =======
# token.split_contents() isn't useful here because this tag doesn't accept variable as arguments
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, list(TemplateTagNode.mapping)))
return TemplateTagNode(tag)
def url(parser, token):
Return an absolute URL matching the given view with its parameters.
This is a way to define links that aren't tied to a particular URL
{% url "url_name" arg1 arg2 %}
{% url "url_name" name1=value1 name2=value2 %}
The first argument is a django.conf.urls.url() name. 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 must be present.
For example, if you have a view ``app_name.views.client_details`` taking
the client's id and the corresponding line in a URLconf looks like this::
url('^client/(\d+)/$', views.client_details, name='client-detail-view')
and this app's URLconf is included into the project's URLconf under some
url('^clients/', include('app_name.urls'))
then in a template you can create a link for a certain client like this::
{% url "client-detail-view" %}
The URL will look like ``/clients/client/123/``.
The first argument may also be the name of a template variable that will be
evaluated to obtain the view name or the URL name, e.g.::
{% with url_name="client-detail-view" %}
{% url url_name %}
{% endwith %}
bits = token.split_contents()
if len(bits) < 2:
raise TemplateSyntaxError("'%s' takes at least one argument, the name of a url()." % 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)
return URLNode(viewname, args, kwargs, asvar)
def verbatim(parser, token):
Stops the template engine from rendering the contents of this block tag.
{% verbatim %}
{% don't process this %}
{% endverbatim %}
You can also designate a specific closing tag block (allowing the
unrendered use of ``{% endverbatim %}``)::
{% verbatim myblock %}
{% endverbatim myblock %}
nodelist = parser.parse(('endverbatim',))
return VerbatimNode(nodelist.render(Context()))
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.png" alt="Bar"
height="10" width="{% widthratio this_value max_value max_width %}" />
If ``this_value`` is 175, ``max_value`` is 200, and ``max_width`` is 100,
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).
In some cases you might want to capture the result of widthratio in a
variable. It can be useful for instance in a blocktrans like this::
{% widthratio this_value max_value max_width as width %}
{% blocktrans %}The width is: {{ width }}{% endblocktrans %}
bits = token.split_contents()
if len(bits) == 4:
tag, this_value_expr, max_value_expr, max_width = bits
asvar = None
elif len(bits) == 6:
tag, this_value_expr, max_value_expr, max_width, as_, asvar = bits
if as_ != 'as':
raise TemplateSyntaxError("Invalid syntax in widthratio tag. Expecting 'as' keyword")
raise TemplateSyntaxError("widthratio takes at least three arguments")
return WidthRatioNode(parser.compile_filter(this_value_expr),
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',))
return WithNode(None, None, nodelist, extra_context=extra_context)