diff --git a/django/template/base.py b/django/template/base.py index b6470f3..37b6fab 100644 --- a/django/template/base.py +++ b/django/template/base.py @@ -901,6 +901,60 @@ class Library(object): else: raise TemplateSyntaxError("Invalid arguments provided to simple_tag") + def assignment_tag(self, func=None, takes_context=None): + def dec(func): + params, xx, xxx, defaults = getargspec(func) + if takes_context: + if params[0] == 'context': + params = params[1:] + else: + raise TemplateSyntaxError("Any tag function decorated with takes_context=True must have a first argument of 'context'") + + class AssignmentNode(Node): + def __init__(self, params_vars, target_var): + self.params_vars = map(Variable, params_vars) + self.target_var = target_var + + def render(self, context): + resolved_vars = [var.resolve(context) for var in self.params_vars] + if takes_context: + func_args = [context] + resolved_vars + else: + func_args = resolved_vars + context[self.target_var] = func(*func_args) + return '' + + def compile_func(parser, token): + bits = token.split_contents() + tag_name = bits[0] + bits = bits[1:] + params_max = len(params) + defaults_length = defaults and len(defaults) or 0 + params_min = params_max - defaults_length + if (len(bits) < 2 or bits[-2] != 'as'): + raise TemplateSyntaxError("'%s' tag takes at least 2 arguments and the second last argument must be 'as'" % tag_name) + params_vars = bits[:-2] + target_var = bits[-1] + if (len(params_vars) < params_min or len(params_vars) > params_max): + if params_min == params_max: + raise TemplateSyntaxError("%s takes %s arguments" % (tag_name, params_min)) + else: + raise TemplateSyntaxError("%s takes between %s and %s arguments" % (tag_name, params_min, params_max)) + return AssignmentNode(params_vars, target_var) + + compile_func.__doc__ = func.__doc__ + self.tag(getattr(func, "_decorated_function", func).__name__, compile_func) + return func + + if func is None: + # @register.assignment_tag(...) + return dec + elif callable(func): + # @register.assignment_tag + return dec(func) + else: + raise TemplateSyntaxError("Invalid arguments provided to assignment_tag") + def inclusion_tag(self, file_name, context_class=Context, takes_context=False): def dec(func): params, xx, xxx, defaults = getargspec(func) diff --git a/docs/howto/custom-template-tags.txt b/docs/howto/custom-template-tags.txt index 7dc6cce..770e823 100644 --- a/docs/howto/custom-template-tags.txt +++ b/docs/howto/custom-template-tags.txt @@ -624,16 +624,18 @@ for example:: Variable resolution will throw a ``VariableDoesNotExist`` exception if it cannot resolve the string passed to it in the current context of the page. +.. _howto-custom-template-tags-simple-tags: + Shortcut for simple tags ~~~~~~~~~~~~~~~~~~~~~~~~ -Many template tags take a number of arguments -- strings or a template variables +Many template tags take a number of arguments -- strings or template variables -- and return a string after doing some processing based solely on the input argument and some external information. For example, the ``current_time`` tag we wrote above is of this variety: we give it a format string, it returns the time as a string. -To ease the creation of the types of tags, Django provides a helper function, +To ease the creation of this type of tags, Django provides a helper function, ``simple_tag``. This function, which is a method of ``django.template.Library``, takes a function that accepts any number of arguments, wraps it in a ``render`` function and the other necessary bits @@ -681,7 +683,66 @@ Or, using decorator syntax:: return your_get_current_time_method(timezone, format_string) For more information on how the ``takes_context`` option works, see the section -on `inclusion tags`_. +on :ref:`inclusion tags`. + +.. _howto-custom-template-tags-assignment-tags: + +Assignment tags +~~~~~~~~~~~~~~~ + +.. versionadded:: 1.4 + +Another common type of template tag is the type that fetches some data and +stores it in a context variable. To ease the creation of this type of tags, +Django provides a helper function, ``assignment_tag``. This function works +the same way as :ref:`simple_tag`, +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:: + +.. code-block:: python + + def get_current_time(format_string): + return datetime.datetime.now().strftime(format_string) + + register.assignment_tag(get_current_time) + +The decorator syntax also works:: + +.. code-block:: python + + @register.assignment_tag + def get_current_time(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:: + +.. code-block:: html+django + + {% get_current_time "%Y-%m-%d %I:%M %p" as the_time %} +

The time is {{ the_time }}.

+ +If your template tag needs to access the current context, you can use the +``takes_context`` argument when registering your tag:: + + # The first argument *must* be called "context" here. + def get_current_time(context, format_string): + timezone = context['timezone'] + return your_get_current_time_method(timezone, format_string) + + register.assignment_tag(takes_context=True)(get_current_time) + +Or, using decorator syntax:: + + @register.assignment_tag(takes_context=True) + def get_current_time(context, format_string): + timezone = context['timezone'] + return your_get_current_time_method(timezone, format_string) + +For more information on how the ``takes_context`` option works, see the section +on :ref:`inclusion tags`. .. _howto-custom-template-tags-inclusion-tags: diff --git a/docs/releases/1.4.txt b/docs/releases/1.4.txt index e86e070..41da2b5 100644 --- a/docs/releases/1.4.txt +++ b/docs/releases/1.4.txt @@ -43,6 +43,14 @@ override the provided templates to change the doctype. A lazily evaluated version of :func:`django.core.urlresolvers.reverse` was added to allow using URL reversals before the project's URLConf gets loaded. +Assignment template tags +~~~~~~~~~~~~~~~~~~~~~~~~ + +A new helper function, +:ref:`assignment_tag`, was added to +``template.Library`` to ease the creation of template tags that store some +data in a specified context variable. + .. _backwards-incompatible-changes-1.4: Backwards incompatible changes in 1.4 diff --git a/tests/regressiontests/templates/custom.py b/tests/regressiontests/templates/custom.py index 7ca359d..5453657 100644 --- a/tests/regressiontests/templates/custom.py +++ b/tests/regressiontests/templates/custom.py @@ -1,3 +1,5 @@ +from __future__ import with_statement + from django import template from django.utils.unittest import TestCase from templatetags import custom @@ -102,3 +104,54 @@ class CustomTagTests(TestCase): c.use_l10n = True self.assertEquals(t.render(c).strip(), u'True') + + def test_assignment_tags(self): + c = template.Context({'value': 42}) + + t = template.Template('{% load custom %}{% assignment_no_params as var %}The result is: {{ var }}') + self.assertEqual(t.render(c), u'The result is: assignment_no_params - Expected result') + + t = template.Template('{% load custom %}{% assignment_one_param 37 as var %}The result is: {{ var }}') + self.assertEqual(t.render(c), u'The result is: assignment_one_param - Expected result: 37') + + t = template.Template('{% load custom %}{% assignment_explicit_no_context 37 as var %}The result is: {{ var }}') + self.assertEqual(t.render(c), u'The result is: assignment_explicit_no_context - Expected result: 37') + + t = template.Template('{% load custom %}{% assignment_no_params_with_context as var %}The result is: {{ var }}') + self.assertEqual(t.render(c), u'The result is: assignment_no_params_with_context - Expected result (context value: 42)') + + t = template.Template('{% load custom %}{% assignment_params_and_context 37 as var %}The result is: {{ var }}') + self.assertEqual(t.render(c), u'The result is: assignment_params_and_context - Expected result (context value: 42): 37') + + with self.assertRaises(template.TemplateSyntaxError) as context_manager: + template.Template('{% load custom %}{% assignment_one_param 37 %}The result is: {{ var }}') + self.assertEqual(context_manager.exception.message, "'assignment_one_param' tag takes at least 2 arguments and the second last argument must be 'as'") + + with self.assertRaises(template.TemplateSyntaxError) as context_manager: + template.Template('{% load custom %}{% assignment_one_param 37 as %}The result is: {{ var }}') + self.assertEqual(context_manager.exception.message, "'assignment_one_param' tag takes at least 2 arguments and the second last argument must be 'as'") + + with self.assertRaises(template.TemplateSyntaxError) as context_manager: + template.Template('{% load custom %}{% assignment_one_param 37 ass var %}The result is: {{ var }}') + self.assertEqual(context_manager.exception.message, "'assignment_one_param' tag takes at least 2 arguments and the second last argument must be 'as'") + + def test_assignment_tag_registration(self): + # Test that the decorators preserve the decorated function's docstring, name and attributes. + self.verify_tag(custom.assignment_no_params, 'assignment_no_params') + self.verify_tag(custom.assignment_one_param, 'assignment_one_param') + self.verify_tag(custom.assignment_explicit_no_context, 'assignment_explicit_no_context') + self.verify_tag(custom.assignment_no_params_with_context, 'assignment_no_params_with_context') + self.verify_tag(custom.assignment_params_and_context, 'assignment_params_and_context') + + def test_assignment_tag_missing_context(self): + # That the 'context' parameter must be present when takes_context is True + def an_assignment_tag_without_parameters(arg): + """Expected __doc__""" + return "Expected result" + + register = template.Library() + decorator = register.assignment_tag(takes_context=True) + + with self.assertRaises(template.TemplateSyntaxError) as context_manager: + decorator(an_assignment_tag_without_parameters) + self.assertEqual(context_manager.exception.message, "Any tag function decorated with takes_context=True must have a first argument of 'context'") diff --git a/tests/regressiontests/templates/templatetags/custom.py b/tests/regressiontests/templates/templatetags/custom.py index 8db113a..2e281f7 100644 --- a/tests/regressiontests/templates/templatetags/custom.py +++ b/tests/regressiontests/templates/templatetags/custom.py @@ -84,3 +84,33 @@ def use_l10n(context): @register.inclusion_tag('test_incl_tag_use_l10n.html', takes_context=True) def inclusion_tag_use_l10n(context): return {} + +@register.assignment_tag +def assignment_no_params(): + """Expected assignment_no_params __doc__""" + return "assignment_no_params - Expected result" +assignment_no_params.anything = "Expected assignment_no_params __dict__" + +@register.assignment_tag +def assignment_one_param(arg): + """Expected assignment_one_param __doc__""" + return "assignment_one_param - Expected result: %s" % arg +assignment_one_param.anything = "Expected assignment_one_param __dict__" + +@register.assignment_tag(takes_context=False) +def assignment_explicit_no_context(arg): + """Expected assignment_explicit_no_context __doc__""" + return "assignment_explicit_no_context - Expected result: %s" % arg +assignment_explicit_no_context.anything = "Expected assignment_explicit_no_context __dict__" + +@register.assignment_tag(takes_context=True) +def assignment_no_params_with_context(context): + """Expected assignment_no_params_with_context __doc__""" + return "assignment_no_params_with_context - Expected result (context value: %s)" % context['value'] +assignment_no_params_with_context.anything = "Expected assignment_no_params_with_context __dict__" + +@register.assignment_tag(takes_context=True) +def assignment_params_and_context(context, arg): + """Expected assignment_params_and_context __doc__""" + return "assignment_params_and_context - Expected result (context value: %s): %s" % (context['value'], arg) +assignment_params_and_context.anything = "Expected assignment_params_and_context __dict__"