Changes between Initial Version and Version 1 of ClassDecoratorTags

Timestamp:

Jan 27, 2010, 7:27:56 PM (14 years ago)

Author:

George Sakkis

Comment:

--

ClassDecoratorTags

@@ +1 @@
+Defining a custom template tag consists of three parts: a compiling function, a rendering `Node` subclass and a tag registration with `register.tag()`. The latter can be used as a (function) decorator on the compiling function, simplifying things into two parts.
+
+A neat fact is that `register.tag()` can actually be used as a class decorator in Python 2.6+ to condense all steps into the `Node` subclass. The compiling function simply becomes the `__init__()` of the class. Here's the 'current_time' tag example from the docs:
+
+{{{
+import datetime
+from django import template
+register = template.Library()
+
+@register.tag('current_time')
+class CurrentTimeNode(template.Node):
+    def __init__(self, parser, token):
+        try:
+            # 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
+        self.format_string = str(format_string[1:-1])
+        
+    def render(self, context):
+        return datetime.datetime.now().strftime(self.format_string)
+}}}
+
+or even simpler, leave off the name argument and use the class name as the tag name:
+
+{{{
+import datetime
+from django import template
+register = template.Library()
+
+@register.tag
+class current_time(template.Node):
+    def __init__(self, parser, token):
+        try:
+            # 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
+        self.format_string = str(format_string[1:-1])
+        
+    def render(self, context):
+        return datetime.datetime.now().strftime(self.format_string)
+}}}