Custom template tags and filters | Django documentation | Django
The web framework for perfectionists with deadlines.
And in your template you would use the following:
{% load poll_extras %}
The app that contains the custom tags must be in
order for the
tag to work. This is a security feature:
It allows you to host Python code for many template libraries on a single host
machine without enabling access to all of them for every Django installation.
There’s no limit on how many modules you put in the templatetags package.
Just keep in mind that a
statement will load
tags/filters for the given Python module name, not the name of the app.
To be a valid tag library, the module must contain a module-level variable
named register that is a template.Library instance, in which all the
tags and filters are registered. So, near the top of your module, put the
following:
from django import template
register = template.Library()
New in Django Development version.
Alternatively, template tag modules can be registered through the
'libraries' argument to
. This is useful if
you want to use a different label from the template tag module name when
loading template tags. It also enables you to register tags without installing
an application.
Behind the scenes
For a ton of examples, read the source code for Django’s default filters
and tags. They’re in django/template/defaultfilters.py and
django/template/defaulttags.py, respectively.
For more information on the
tag, read its documentation.
Writing custom template filters
Custom filters are just Python functions that take one or two arguments:
The value of the variable (input) – not necessarily a string.
The value of the argument – this can have a default value, or be left
out altogether.
For example, in the filter {{ var|foo:&bar& }}, the filter foo would be
passed the variable var and the argument &bar&.
Since the template language doesn’t provide exception handling, any exception
raised from a template filter will be exposed as a server error. Thus, filter
functions should avoid raising exceptions if there is a reasonable fallback
value to return. In case of input that represents a clear bug in a template,
raising an exception may still be better than silent failure which hides the
Here’s an example filter definition:
def cut(value, arg):
&&&Removes all values of arg from the given string&&&
return value.replace(arg, '')
And here’s an example of how that filter would be used:
{{ somevariable|cut:&0& }}
Most filters don’t take arguments. In this case, just leave the argument out of
your function. Example:
def lower(value): # Only one argument.
&&&Converts a string into all lowercase&&&
return value.lower()
Registering custom filters
django.template.Library.filter()
Once you’ve written your filter definition, you need to register it with
your Library instance, to make it available to Django’s template language:
register.filter('cut', cut)
register.filter('lower', lower)
The Library.filter() method takes two arguments:
The name of the filter – a string.
The compilation function – a Python function (not the name of the
function as a string).
You can use register.filter() as a decorator instead:
@register.filter(name='cut')
def cut(value, arg):
return value.replace(arg, '')
@register.filter
def lower(value):
return value.lower()
If you leave off the name argument, as in the second example above, Django
will use the function’s name as the filter name.
Finally, register.filter() also accepts three keyword arguments,
is_safe, needs_autoescape, and expects_localtime. These arguments
are described in
Template filters that expect strings
django.template.defaultfilters.stringfilter()
If you’re writing a template filter that only expects a string as the first
argument, you should use the decorator stringfilter. This will
convert an object to its string value before being passed to your function:
from django import template
from django.template.defaultfilters import stringfilter
register = template.Library()
@register.filter
@stringfilter
def lower(value):
return value.lower()
This way, you’ll be able to pass, say, an integer to this filter, and it
won’t cause an AttributeError (because integers don’t have lower()
Filters and auto-escaping
When writing a custom filter, give some thought to how the filter will interact
with Django’s auto-escaping behavior. Note that three types of strings can be
passed around inside the template code:
Raw strings are the native Python str or unicode types. On
output, they’re escaped if auto-escaping is in effect and presented
unchanged, otherwise.
Safe strings are strings that have been marked safe from further
escaping at output time. Any necessary escaping has already been done.
They’re commonly used for output that contains raw HTML that is intended
to be interpreted as-is on the client side.
Internally, these strings are of type SafeBytes or SafeText.
They share a common base class of SafeData, so you can test
for them using code like:
if isinstance(value, SafeData):
# Do something with the &safe& string.
Strings marked as “needing escaping” are always escaped on
output, regardless of whether they are in an
not. These strings are only escaped once, however, even if auto-escaping
Internally, these strings are of type EscapeBytes or
EscapeText. Generally you don’t have
exist for the implementation of the
Template filter code falls into one of two situations:
Your filter does not introduce any HTML-unsafe characters (&, &,
', & or &) into the result that were not already present. In
this case, you can let Django take care of all the auto-escaping
handling for you. All you need to do is set the is_safe flag to True
when you register your filter function, like so:
@register.filter(is_safe=True)
def myfilter(value):
return value
This flag tells Django that if a “safe” string is passed into your
filter, the result will still be “safe” and if a non-safe string is
passed in, Django will automatically escape it, if necessary.
You can think of this as meaning “this filter is safe – it doesn’t
introduce any possibility of unsafe HTML.”
The reason is_safe is necessary is because there are plenty of
normal string operations that will turn a SafeData object back into
a normal str or unicode object and, rather than try to catch
them all, which would be very difficult, Django repairs the damage after
the filter has completed.
For example, suppose you have a filter that adds the string xx to
the end of any input. Since this introduces no dangerous HTML characters
to the result (aside from any that were already present), you should
mark your filter with is_safe:
@register.filter(is_safe=True)
def add_xx(value):
return '%sxx' % value
When this filter is used in a template where auto-escaping is enabled,
Django will escape the output whenever the input is not already marked
as “safe”.
By default, is_safe is False, and you can omit it from any filters
where it isn’t required.
Be careful when deciding if your filter really does leave safe strings
as safe. If you’re removing characters, you might inadvertently leave
unbalanced HTML tags or entities in the result. For example, removing a
& from the input might turn &a& into &a, which would need to
be escaped on output to avoid causing problems. Similarly, removing a
semicolon (;) can turn & into &amp, which is no longer a
valid entity and thus needs further escaping. Most cases won’t be nearly
this tricky, but keep an eye out for any problems like that when
reviewing your code.
Marking a filter is_safe will coerce the filter’s return value to
If your filter should return a boolean or other non-string
value, marking it is_safe will probably have unintended
consequences (such as converting a boolean False to the string
‘False’).
Alternatively, your filter code can manually take care of any necessary
escaping. This is necessary when you’re introducing new HTML markup into
the result. You want to mark the output as safe from further
escaping so that your HTML markup isn’t escaped further, so you’ll need
to handle the input yourself.
To mark the output as a safe string, use
Be careful, though. You need to do more than just mark the output as
safe. You need to ensure it really is safe, and what you do depends on
whether auto-escaping is in effect. The idea is to write filters that
can operate in templates where auto-escaping is either on or off in
order to make things easier for your template authors.
In order for your filter to know the current auto-escaping state, set the
needs_autoescape flag to True when you register your filter function.
(If you don’t specify this flag, it defaults to False). This flag tells
Django that your filter function wants to be passed an extra keyword
argument, called autoescape, that is True if auto-escaping is in
effect and False otherwise. It is recommended to set the default of the
autoescape parameter to True, so that if you call the function
from Python code it will have escaping enabled by default.
For example, let’s write a filter that emphasizes the first character of
from django import template
from django.utils.html import conditional_escape
from django.utils.safestring import mark_safe
register = template.Library()
@register.filter(needs_autoescape=True)
def initial_letter_filter(text, autoescape=True):
first, other = text[0], text[1:]
if autoescape:
esc = conditional_escape
esc = lambda x: x
result = '&strong&%s&/strong&%s' % (esc(first), esc(other))
return mark_safe(result)
The needs_autoescape flag and the autoescape keyword argument mean
that our function will know whether automatic escaping is in effect when the
filter is called. We use autoescape to decide whether the input data
needs to be passed through django.utils.html.conditional_escape or not.
(In the latter case, we just use the identity function as the “escape”
function.) The conditional_escape() function is like escape() except
it only escapes input that is not a SafeData instance. If a
SafeData instance is passed to conditional_escape(), the data is
returned unchanged.
Finally, in the above example, we remember to mark the result as safe
so that our HTML is inserted directly into the template without further
There’s no need to worry about the is_safe flag in this case
(although including it wouldn’t hurt anything). Whenever you manually
handle the auto-escaping issues and return a safe string, the
is_safe flag won’t change anything either way.
Avoiding XSS vulnerabilities when reusing built-in filters
Changed in Django 1.8.
Django’s built-in filters have autoescape=True by default in order to
get the proper autoescaping behavior and avoid a cross-site script
vulnerability.
In older versions of Django, be careful when reusing Django’s built-in
filters as autoescape defaults to None. You’ll need to pass
autoescape=True to get autoescaping.
For example, if you wanted to write a custom filter called
urlize_and_linebreaks that combined the
filters, the filter would look like:
from django.template.defaultfilters import linebreaksbr, urlize
@register.filter(needs_autoescape=True)
def urlize_and_linebreaks(text, autoescape=True):
return linebreaksbr(
urlize(text, autoescape=autoescape),
autoescape=autoescape
{{ comment|urlize_and_linebreaks }}
would be equivalent to:
{{ comment|urlize|linebreaksbr }}
When this flag is set, if the first argument to your filter is a time zone
aware datetime, Django will convert it to the current time zone before passing
it to your filter when appropriate, according to .
A few things to note about the simple_tag helper function:
Checking for the required number of arguments, etc., has already been
done by the time our function is called, so we don’t need to do that.
The quotes around the argument (if any) have already been stripped away,
so we just receive a plain string.
If the argument was a template variable, our function is passed the
current value of the variable, not the variable itself.
If your template tag needs to access the current context, you can use the
takes_context argument when registering your tag:
@register.simple_tag(takes_context=True)
def current_time(context, format_string):
timezone = context['timezone']
return your_get_current_time_method(timezone, format_string)
Note that the first argument must be called context.
For more information on how the takes_context option works, see the section
If you need to rename your tag, you can provide a custom name for it:
register.simple_tag(lambda x: x - 1, name='minusone')
@register.simple_tag(name='minustwo')
def some_function(value):
return value - 2
simple_tag functions may accept any number of positional or keyword
arguments. For example:
@register.simple_tag
def my_tag(a, b, *args, **kwargs):
warning = kwargs['warning']
profile = kwargs['profile']
return ...
Then in the template any number of arguments, separated by spaces, may be
passed to the template tag. Like in Python, the values for keyword arguments
are set using the equal sign (“=”) and must be provided after the
positional arguments. For example:
{% my_tag 123 &abcd& book.title warning=message|lower profile=user.profile %}
New in Django Development version.
It’s possible to store the tag results in a template variable rather than
directly outputting it. This is done by using the as argument followed by
the variable name. Doing so enables you to output the content yourself where
you see fit:
{% get_current_time &%Y-%m-%d %I:%M %p& as the_time %}
&p&The time is {{ the_time }}.&/p&
...and the output will be something like this:
&li&First choice&/li&
&li&Second choice&/li&
&li&Third choice&/li&
First, define the function that takes the argument and produces a dictionary of
data for the result. The important point here is we only need to return a
dictionary, not anything more complex. This will be used as a template context
for the template fragment. Example:
def show_results(poll):
choices = poll.choice_set.all()
return {'choices': choices}
Next, create the template used to render the tag’s output. This template is a
fixed feature of the tag: the tag writer specifies it, not the template
designer. Following our example, the template is very simple:
{% for choice in choices %}
&li& {{ choice }} &/li&
{% endfor %}
Now, create and register the inclusion tag by calling the inclusion_tag()
method on a Library object. Following our example, if the above template is
in a file called results.html in a directory that’s searched by the
template loader, we’d register the tag like this:
# Here, register is a django.template.Library instance, as before
@register.inclusion_tag('results.html')
def show_results(poll):
Alternatively it is possible to register the inclusion tag using a
from django.template.loader import get_template
t = get_template('results.html')
register.inclusion_tag(t)(show_results)
...when first creating the function.
Sometimes, your inclusion tags might require a large number of arguments,
making it a pain for template authors to pass in all the arguments and remember
their order. To solve this, Django provides a takes_context option for
inclusion tags. If you specify takes_context in creating a template tag,
the tag will have no required arguments, and the underlying Python function
will have one argument – the template context as of when the tag was called.
For example, say you’re writing an inclusion tag that will always be used in a
context that contains home_link and home_title variables that point
back to the main page. Here’s what the Python function would look like:
@register.inclusion_tag('link.html', takes_context=True)
def jump_link(context):
'link': context['home_link'],
'title': context['home_title'],
Note that the first parameter to the function must be called context.
In that register.inclusion_tag() line, we specified takes_context=True
and the name of the template. Here’s what the template link.html might look
Jump directly to &a href=&{{ link }}&&{{ title }}&/a&.
Then, any time you want to use that custom tag, load its library and call it
without any arguments, like so:
{% jump_link %}
Note that when you’re using takes_context=True, there’s no need to pass
arguments to the template tag. It automatically gets access to the context.
The takes_context parameter defaults to False. When it’s set to
True, the tag is passed the context object, as in this example. That’s the
only difference between this case and the previous inclusion_tag example.
inclusion_tag functions may accept any number of positional or keyword
arguments. For example:
@register.inclusion_tag('my_template.html')
def my_tag(a, b, *args, **kwargs):
warning = kwargs['warning']
profile = kwargs['profile']
return ...
Then in the template any number of arguments, separated by spaces, may be
passed to the template tag. Like in Python, the values for keyword arguments
are set using the equal sign (“=”) and must be provided after the
positional arguments. For example:
{% my_tag 123 &abcd& book.title warning=message|lower profile=user.profile %}
To ease the creation of tags setting a variable in the context, Django provides
a helper function, assignment_tag. This function works the same way as
except that it stores the tag’s
result in a specified context variable instead of directly outputting it.
Our earlier current_time function could thus be written like this:
@register.assignment_tag
def get_current_time(format_string):
return datetime.datetime.now().strftime(format_string)
You may then store the result in a template variable using the as argument
followed by the variable name, and output it yourself where you see fit:
{% get_current_time &%Y-%m-%d %I:%M %p& as the_time %}
&p&The time is {{ the_time }}.&/p&
A quick overview
The template system works in a two-step process: compiling and rendering. To
define a custom template tag, you specify how the compilation works and how
the rendering works.
When Django compiles a template, it splits the raw template text into
‘’nodes’‘. Each node is an instance of django.template.Node and has
a render() method. A compiled template is, simply, a list of Node
objects. When you call render() on a compiled template object, the template
calls render() on each Node in its node list, with the given context.
The results are all concatenated together to form the output of the template.
Thus, to define a custom template tag, you specify how the raw template tag is
converted into a Node (the compilation function), and what the node’s
render() method does.
Writing the compilation function
For each template tag the template parser encounters, it calls a Python
function with the tag contents and the parser object itself. This function is
responsible for returning a Node instance based on the contents of the tag.
For example, let’s write a full implementation of our simple template tag,
{% current_time %}, that displays the current date/time, formatted according
to a parameter given in the tag, in
syntax. It’s a good
idea to decide the tag syntax before anything else. In our case, let’s say the
tag should be used like this:
&p&The time is {% current_time &%Y-%m-%d %I:%M %p& %}.&/p&
The parser for this function should grab the parameter and create a Node
from django import template
def do_current_time(parser, token):
# split_contents() knows not to split quoted strings.
tag_name, format_string = token.split_contents()
except ValueError:
raise template.TemplateSyntaxError(
&%r tag requires a single argument& % token.contents.split()[0]
if not (format_string[0] == format_string[-1] and format_string[0] in ('&', &'&)):
raise template.TemplateSyntaxError(
&%r tag's argument should be in quotes& % tag_name
return CurrentTimeNode(format_string[1:-1])
parser is the template parser object. We don’t need it in this
token.contents is a string of the raw contents of the tag. In our
example, it’s 'current_time &%Y-%m-%d %I:%M %p&'.
The token.split_contents() method separates the arguments on spaces
while keeping quoted strings together. The more straightforward
token.contents.split() wouldn’t be as robust, as it would naively
split on all spaces, including those within quoted strings. It’s a good
idea to always use token.split_contents().
This function is responsible for raising
django.template.TemplateSyntaxError, with helpful messages, for
any syntax error.
The TemplateSyntaxError exceptions use the tag_name variable.
Don’t hard-code the tag’s name in your error messages, because that
couples the tag’s name to your function. token.contents.split()[0]
will ‘’always’’ be the name of your tag – even when the tag has no
arguments.
The function returns a CurrentTimeNode with everything the node needs
to know about this tag. In this case, it just passes the argument –
&%Y-%m-%d %I:%M %p&. The leading and trailing quotes from the
template tag are removed in format_string[1:-1].
The parsing is very low-level. The Django developers have experimented
with writing small frameworks on top of this parsing system, using
techniques such as EBNF grammars, but those experiments made the template
engine too slow. It’s low-level because that’s fastest.
Writing the renderer
The second step in writing custom tags is to define a Node subclass that
has a render() method.
Continuing the above example, we need to define CurrentTimeNode:
import datetime
from django import template
class CurrentTimeNode(template.Node):
def __init__(self, format_string):
self.format_string = format_string
def render(self, context):
return datetime.datetime.now().strftime(self.format_string)
__init__() gets the format_string from do_current_time().
Always pass any options/parameters/arguments to a Node via its
__init__().
The render() method is where the work actually happens.
render() should generally fail silently, particularly in a production
environment. In some cases however, particularly if
context.template.engine.debug is True, this method may raise an
exception to make debugging easier. For example, several core tags raise
django.template.TemplateSyntaxError if they receive the wrong number or
type of arguments.
Ultimately, this decoupling of compilation and rendering results in an
efficient template system, because a template can render multiple contexts
without having to be parsed multiple times.
This is not a very common situation, but it’s useful if you’re rendering a
template yourself. For example:
def render(self, context):
t = context.template.engine.get_template('small_fragment.html')
return t.render(Context({'var': obj}, autoescape=context.autoescape))
Changed in Django 1.8: The template attribute of Context objects was added in Django 1.8.
must be used instead of
because the latter now returns
a wrapper whose render method doesn’t accept a
If we had neglected to pass in the current context.autoescape value to our
new Context in this example, the results would have always been
automatically escaped, which may not be the desired behavior if the template
tag is used inside a
A naive implementation of CycleNode might look something like this:
import itertools
from django import template
class CycleNode(template.Node):
def __init__(self, cyclevars):
self.cycle_iter = itertools.cycle(cyclevars)
def render(self, context):
return next(self.cycle_iter)
But, suppose we have two templates rendering the template snippet from above at
the same time:
Thread 1 performs its first loop iteration, CycleNode.render()
returns ‘row1’
Thread 2 performs its first loop iteration, CycleNode.render()
returns ‘row2’
Thread 1 performs its second loop iteration, CycleNode.render()
returns ‘row1’
Thread 2 performs its second loop iteration, CycleNode.render()
returns ‘row2’
The CycleNode is iterating, but it’s iterating globally. As far as Thread 1
and Thread 2 are concerned, it’s always returning the same value. This is
obviously not what we want!
To address this problem, Django provides a render_context that’s associated
with the context of the template that is currently being rendered. The
render_context behaves like a Python dictionary, and should be used to
store Node state between invocations of the render method.
Let’s refactor our CycleNode implementation to use the render_context:
class CycleNode(template.Node):
def __init__(self, cyclevars):
self.cyclevars = cyclevars
def render(self, context):
if self not in context.render_context:
context.render_context[self] = itertools.cycle(self.cyclevars)
cycle_iter = context.render_context[self]
return next(cycle_iter)
Note that it’s perfectly safe to store global information that will not change
throughout the life of the Node as an attribute. In the case of
CycleNode, the cyclevars argument doesn’t change after the Node is
instantiated, so we don’t need to put it in the render_context. But state
information that is specific to the template that is currently being rendered,
like the current iteration of the CycleNode, should be stored in the
render_context.
Notice how we used self to scope the CycleNode specific information
within the render_context. There may be multiple CycleNodes in a
given template, so we need to be careful not to clobber another node’s
state information. The easiest way to do this is to always use self as
the key into render_context. If you’re keeping track of several state
variables, make render_context[self] a dictionary.
The tag() method takes two arguments:
The name of the template tag – a string. If this is left out, the
name of the compilation function will be used.
The compilation function – a Python function (not the name of the
function as a string).
As with filter registration, it is also possible to use this as a decorator:
@register.tag(name=&current_time&)
def do_current_time(parser, token):
@register.tag
def shout(parser, token):
If you leave off the name argument, as in the second example above, Django
will use the function’s name as the tag name.
Initially, token.split_contents() will return three values:
The tag name format_time.
The string 'blog_entry.date_updated' (without the surrounding
The formatting string '&%Y-%m-%d %I:%M %p&'. The return value from
split_contents() will include the leading and trailing quotes for
string literals like this.
Now your tag should begin to look like this:
from django import template
def do_format_time(parser, token):
# split_contents() knows not to split quoted strings.
tag_name, date_to_be_formatted, format_string = token.split_contents()
except ValueError:
raise template.TemplateSyntaxError(
&%r tag requires exactly two arguments& % token.contents.split()[0]
if not (format_string[0] == format_string[-1] and format_string[0] in ('&', &'&)):
raise template.TemplateSyntaxError(
&%r tag's argument should be in quotes& % tag_name
return FormatTimeNode(date_to_be_formatted, format_string[1:-1])
You also have to change the renderer to retrieve the actual contents of the
date_updated property of the blog_entry object.
This can be
accomplished by using the Variable() class in django.template.
To use the Variable class, simply instantiate it with the name of the
variable to be resolved, and then call variable.resolve(context). So,
for example:
class FormatTimeNode(template.Node):
def __init__(self, date_to_be_formatted, format_string):
self.date_to_be_formatted = template.Variable(date_to_be_formatted)
self.format_string = format_string
def render(self, context):
actual_date = self.date_to_be_formatted.resolve(context)
return actual_date.strftime(self.format_string)
except template.VariableDoesNotExist:
return ''
Variable resolution will throw a VariableDoesNotExist exception if it
cannot resolve the string passed to it in the current context of the page.
Setting a variable in the context
The above examples simply output a value. Generally, it’s more flexible if your
template tags set template variables instead of outputting values. That way,
template authors can reuse the values that your template tags create.
To set a variable in the context, just use dictionary assignment on the context
object in the render() method. Here’s an updated version of
CurrentTimeNode that sets a template variable current_time instead of
outputting it:
import datetime
from django import template
class CurrentTimeNode2(template.Node):
def __init__(self, format_string):
self.format_string = format_string
def render(self, context):
context['current_time'] = datetime.datetime.now().strftime(self.format_string)
return ''
Note that render() returns the empty string. render() should always
return string output. If all the template tag does is set a variable,
render() should return the empty string.
Here’s how you’d use this new version of the tag:
{% current_time &%Y-%M-%d %I:%M %p& %}&p&The time is {{ current_time }}.&/p&
Variable scope in context
Any variable set in the context will only be available in the same
block of the template in which it was assigned. This behavior is
it provides a scope for variables so that they don’t conflict
with context in other blocks.
But, there’s a problem with CurrentTimeNode2: The variable name
current_time is hard-coded. This means you’ll need to make sure your
template doesn’t use {{ current_time }} anywhere else, because the
{% current_time %} will blindly overwrite that variable’s value. A cleaner
solution is to make the template tag specify the name of the output variable,
{% current_time &%Y-%M-%d %I:%M %p& as my_current_time %}
&p&The current time is {{ my_current_time }}.&/p&
To do that, you’ll need to refactor both the compilation function and Node
class, like so:
class CurrentTimeNode3(template.Node):
def __init__(self, format_string, var_name):
self.format_string = format_string
self.var_name = var_name
def render(self, context):
context[self.var_name] = datetime.datetime.now().strftime(self.format_string)
return ''
def do_current_time(parser, token):
# This version uses a regular expression to parse tag contents.
# Splitting by None == splitting by spaces.
tag_name, arg = token.contents.split(None, 1)
except ValueError:
raise template.TemplateSyntaxError(
&%r tag requires arguments& % token.contents.split()[0]
m = re.search(r'(.*?) as (\w+)', arg)
raise template.TemplateSyntaxError(&%r tag had invalid arguments& % tag_name)
format_string, var_name = m.groups()
if not (format_string[0] == format_string[-1] and format_string[0] in ('&', &'&)):
raise template.TemplateSyntaxError(
&%r tag's argument should be in quotes& % tag_name
return CurrentTimeNode3(format_string[1:-1], var_name)
The difference here is that do_current_time() grabs the format string and
the variable name, passing both to CurrentTimeNode3.
Finally, if you only need to have a simple syntax for your custom
context-updating template tag, you might want to consider using the
we introduced above.
The actual implementation of
is slightly
different in that it allows broken template tags to appear between
{% comment %} and {% endcomment %}. It does so by calling
parser.skip_past('endcomment') instead of parser.parse(('endcomment',))
followed by parser.delete_first_token(), thus avoiding the generation of a
node list.
parser.parse() takes a tuple of names of block tags ‘’to parse until’‘. It
returns an instance of django.template.NodeList, which is a list of
all Node objects that the parser encountered ‘’before’’ it encountered
any of the tags named in the tuple.
In &nodelist = parser.parse(('endcomment',))& in the above example,
nodelist is a list of all nodes between the {% comment %} and
{% endcomment %}, not counting {% comment %} and {% endcomment %}
themselves.
After parser.parse() is called, the parser hasn’t yet “consumed” the
{% endcomment %} tag, so the code needs to explicitly call
parser.delete_first_token().
CommentNode.render() simply returns an empty string. Anything between
{% comment %} and {% endcomment %} is ignored.
As in the previous example, we’ll use parser.parse(). But this time, we
pass the resulting nodelist to the Node:
def do_upper(parser, token):
nodelist = parser.parse(('endupper',))
parser.delete_first_token()
return UpperNode(nodelist)
class UpperNode(template.Node):
def __init__(self, nodelist):
self.nodelist = nodelist
def render(self, context):
output = self.nodelist.render(context)
return output.upper()
The only new concept here is the self.nodelist.render(context) in
UpperNode.render().
For more examples of complex rendering, see the source code of
in django/template/defaulttags.py and
in django/template/smartif.py.
Additional Information
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Handy when looking for specific information.
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Ask a question in the #django IRC channel, or search the IRC logs to see if it’s been asked before.
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