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Fixed #2655 -- added documentation about resolve_variable() for custo…

…m template

tags. Thanks

git-svn-id: bcc190cf-cafb-0310-a4f2-bffc1f526a37
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1 parent 007f17d commit fefcbbfe3719eaf0b493eabaab591c0b7bc35d9e @malcolmt malcolmt committed Feb 10, 2007
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  1. +1 −0 AUTHORS
  2. +64 −0 docs/templates_python.txt
@@ -66,6 +66,7 @@ answer newbie questions, and generally made Django that much better:
Matt Croydon <>
Jonathan Daugherty (cygnus) <>
Jason Davies (Esaj) <>
Alex Dedul
@@ -801,6 +801,70 @@ Python 2.4 and above::
If you leave off the ``name`` argument, as in the second example above, Django
will use the function's name as the tag name.
+Passing template variables to the tag
+Although you can pass any number of arguments to a template tag using
+``token.split_contents()``, the arguments are all unpacked as
+string literals. A little more work is required in order to dynamic content (a
+template variable) to a template tag as an argument.
+While the previous examples have formatted the current time into a string and
+returned the string, suppose you wanted to pass in a ``DateTimeField`` from an
+object and have the template tag format that date-time::
+ <p>This post was last updated at {% format_time blog_entry.date_updated "%Y-%m-%d %I:%M %p" %}.</p>
+Initially, ``token.split_contents()`` will return three values:
+ 1. The tag name ``format_time``.
+ 2. The string "blog_entry.date_updated" (without the surrounding quotes).
+ 3. 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):
+ try:
+ # split_contents() knows not to split quoted strings.
+ tag_name, date_to_format, format_string = token.split_contents()
+ except ValueError:
+ raise template.TemplateSyntaxError, "%r tag requires exactly two arguments" % token.contents[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_format, 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 ``resolve_variable()`` function in
+``django.template``. You pass ``resolve_variable()`` the variable name and the
+current context, available in the ``render`` method::
+ from django import template
+ from django.template import resolve_variable
+ import datetime
+ class FormatTimeNode(template.Node):
+ def __init__(self, date_to_format, format_string):
+ self.date_to_format = date_to_format
+ self.format_string = format_string
+ def render(self, context):
+ try:
+ actual_date = resolve_variable(self.date_to_format, context)
+ return actual_date.strftime(self.format_string)
+ except VariableDoesNotExist:
+ return ''
+``resolve_variable`` will try to resolve ``blog_entry.date_updated`` and then
+format it accordingly.
+.. note::
+ The ``resolve_variable()`` function will throw a ``VariableDoesNotExist``
+ exception if it cannot resolve the string passed to it in the current
+ context of the page.
Shortcut for simple tags

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