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Partially render in Jinja

 2 years ago
source link: https://www.chunyangwen.com/blog/python/jinja-partial-template.html
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Partially render in Jinja

Posted by chunyang on June 7, 2022
TAGS: #python

A Jinja template can be rendered. Sometimes the data we need can not be collected in just one place. It will be helpful if we can render a template multiple times.

By default, a Jinja template can not be rendered multiple times. It will raise an exception or insert null values into the corresponding placeholders.

In the blog, we will use a trick to mimic the partially rendering behavior. Jinja has an operator raw which can be used to render its original content.

from jinja2 import Template
template_str = """
{% raw %} {%  raw  %} 

{{hi}}

 {%  endraw  %} 
"""

partial_template_str = Template(template_str).render()

result = Template(partial_template_str).render(hi=3)

But using raw will introduce redundant newlines. We can not use - to remove the spaces. It is wrong sometimes we remove the leading spaces.

from jinja2 import Template
template_str = """
{% raw %}

{{hi}}

{% endraw %}
"""

partial_template_str = Template(template_str, trim_blocks=True, lstrip_blocks=True).render()

result = Template(partial_template_str).render(hi=3)
print(result)

If the leading spaces are not meaningless to your program, you can use - to remove them. Referecne

from jinja2 import Template
template_str = """
{% raw -%}

{{hi}}

{% endraw %}
"""

partial_template_str = Template(template_str, trim_blocks=True, lstrip_blocks=True).render()

result = Template(partial_template_str).render(hi=3)
print(result)

If we need more nested templates, such as we want a template to be rendered three or more times, the code will be ugly. It seems that Jinja does not provide way to implement a customized operator

from jinja2 import Template
template_str = """
{% raw -%}

{{hi}}

{% endraw -%}


{{'{%'}} raw {{'%}'}}


{{hello}}


{{'{%'}} endraw {{'%}'}}


"""

partial_template_str = Template(template_str, trim_blocks=True, lstrip_blocks=True).render()
print(partial_template_str)
print("=" * 10)

result = Template(partial_template_str).render(hi=3)
print(result)
print("=" * 10)

final_result = Template(result).render(hello=4)
print(final_result)

raw and endraw can not be nested. You are not allowed to insert raw and endraw block in another raw and endraw block`.


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