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Template tag for stripping blank lines

Author:
akaihola
Posted:
January 29, 2008
Language:
Python
Version:
.96
Tags:
template html strip empty blank
Score:
2 (after 2 ratings)

When writing clean and easy-to-read templates, it's usually good to have structural template tags (e.g. {%for%}, {%if%}) alone on their own line with proper indentation.

When such a template is rendered, the resulting HTML will have blank lines in place of the template tags. The leading blank space used for indentation is also intact.

This template tag strips all empty and all-whitespace lines when rendering the template. Be careful not to apply it when not intended, e.g. when empty lines are wanted inside PRE tags.

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import re

from django.utils.functional import allow_lazy
from django.utils.encoding import force_unicode
from django.template import Node, Library

register = Library()

def strip_empty_lines(value):
    """Return the given HTML with empty and all-whitespace lines removed."""
    return re.sub(r'\n[ \t]*(?=\n)', '', force_unicode(value))
strip_empty_lines = allow_lazy(strip_empty_lines, unicode)

class GaplessNode(Node):
    def __init__(self, nodelist):
        self.nodelist = nodelist

    def render(self, context):
        return strip_empty_lines(self.nodelist.render(context).strip())

def gapless(parser, token):
    """
    Remove empty and whitespace-only lines.  Useful for getting rid of those
    empty lines caused by template lines with only template tags and possibly
    whitespace.

    Example usage::

        <p>{% gapless %}
          {% if yepp %}
            <a href="foo/">Foo</a>
          {% endif %}
        {% endgapless %}</p>

    This example would return this HTML::

        <p>
            <a href="foo/">Foo</a>
        </p>

    """
    nodelist = parser.parse(('endgapless',))
    parser.delete_first_token()
    return GaplessNode(nodelist)
gapless = register.tag(gapless)

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Comments

akaihola (on February 25, 2008):

mikko, strange that I didn't find your snippet when I tried to search for one before writing mine.

Actually I think this solution, where blank lines are removed after rendering the lines, is not optimal, because also blank lines inserted on purpose are now lost.

It would be neat if lines with nothing but a template tag (and blank space) were detected and stripped of whitespace and the line feed. I don't have an idea how to implement that though. Probably also tags with non-empty output should retain their indentation.

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