mirror of https://gitee.com/openkylin/jinja2.git
101 lines
3.1 KiB
ReStructuredText
101 lines
3.1 KiB
ReStructuredText
Tips and Tricks
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===============
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.. highlight:: html+jinja
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This part of the documentation shows some tips and tricks for Jinja
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templates.
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.. _null-default-fallback:
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Null-Default Fallback
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---------------------
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Jinja supports dynamic inheritance and does not distinguish between parent
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and child template as long as no `extends` tag is visited. While this leads
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to the surprising behavior that everything before the first `extends` tag
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including whitespace is printed out instead of being ignored, it can be used
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for a neat trick.
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Usually child templates extend from one template that adds a basic HTML
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skeleton. However it's possible to put the `extends` tag into an `if` tag to
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only extend from the layout template if the `standalone` variable evaluates
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to false which it does per default if it's not defined. Additionally a very
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basic skeleton is added to the file so that if it's indeed rendered with
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`standalone` set to `True` a very basic HTML skeleton is added::
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{% if not standalone %}{% extends 'default.html' %}{% endif -%}
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<!DOCTYPE html>
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<title>{% block title %}The Page Title{% endblock %}</title>
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<link rel="stylesheet" href="style.css" type="text/css">
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{% block body %}
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<p>This is the page body.</p>
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{% endblock %}
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Alternating Rows
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----------------
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If you want to have different styles for each row of a table or
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list you can use the `cycle` method on the `loop` object::
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<ul>
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{% for row in rows %}
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<li class="{{ loop.cycle('odd', 'even') }}">{{ row }}</li>
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{% endfor %}
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</ul>
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`cycle` can take an unlimited number of strings. Each time this
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tag is encountered the next item from the list is rendered.
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Highlighting Active Menu Items
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------------------------------
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Often you want to have a navigation bar with an active navigation
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item. This is really simple to achieve. Because assignments outside
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of `block`\s in child templates are global and executed before the layout
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template is evaluated it's possible to define the active menu item in the
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child template::
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{% extends "layout.html" %}
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{% set active_page = "index" %}
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The layout template can then access `active_page`. Additionally it makes
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sense to define a default for that variable::
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{% set navigation_bar = [
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('/', 'index', 'Index'),
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('/downloads/', 'downloads', 'Downloads'),
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('/about/', 'about', 'About')
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] -%}
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{% set active_page = active_page|default('index') -%}
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...
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<ul id="navigation">
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{% for href, id, caption in navigation_bar %}
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<li{% if id == active_page %} class="active"{% endif %}>
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<a href="{{ href|e }}">{{ caption|e }}</a></li>
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{% endfor %}
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</ul>
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...
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.. _accessing-the-parent-loop:
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Accessing the parent Loop
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-------------------------
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The special `loop` variable always points to the innermost loop. If it's
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desired to have access to an outer loop it's possible to alias it::
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<table>
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{% for row in table %}
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<tr>
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{% set rowloop = loop %}
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{% for cell in row %}
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<td id="cell-{{ rowloop.index }}-{{ loop.index }}">{{ cell }}</td>
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{% endfor %}
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</tr>
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{% endfor %}
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</table>
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