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• Jinja2 templating tutorial.
• The tutorial can be found here, https://realpython.com/blog/python/primer-on-jinja-templating/.
• Flask is using Jinja2 as its templating engine.
• The cool thing about Jinja2 is that it is using .html extension.
• The command to install Jinja2 is sudo pip3 install jinja2 or if in virtual environment the command will be pip3 install jinja2.
• Anyway, if you install Flask from pip it would also install Jinja2 automatically.
• Jinja2 is part of from flask import render_template.
• You can put any arbitrary variables in the HTML template using render_template() function. This is an example.

@app.route("/")
def index():
    render_template(
        "which_template_you_want_to_use.html",
        any_variable_1="any_value_although_it_is_usually_string",
        any_variable_2="any_value_although_it_is_usually_string",
        any_variable_3="any_value_although_it_is_usually_string",
        any_variable_4="any_value_although_it_is_usually_string",
        any_variable_5="any_value_although_it_is_usually_string"
    )

• Then these variables can be called in the template "which_template_you_want_to_use.html" with {{any_variable_1}}.
• This is an example specifically for Flask.
• There is template inheritance as well.
  • The sub - template is what usually the main display as it is the same case with which_template_you_want_to_use.html.
  • The super template is the main template (the larger HTML files with all CSS and JS files attached into it) that will be added with functionalities from the sub - template.
• So in analogous, super template is the function and the sub - template is the arguments.
• But needed to be known that argument can be a function as well.
• Hence, this can be further dumbed down into several sub - template.
• There is block tag like this, {% block %} this is meant for the sub - template to fill and for super template to reference which part of it got filled by child template.
• Example {% block %} in sub - template.

{% block this_from_sub_template %}
  {# Put some HTML or Jinja2 codes here. #}
{% endblock %}

• Example {% block %} in super template.

{% block this_from_sub_template %}
{% endblock %}

• In super template we just do not fill anything in between of the Jinja2 tag.
• Do not forget to put {% extends "the_super_template.html" %} in the uppermost of the sub - template.
• If you need to render a block from super template then use this {{super()}}. This is the example codes.

{# These codes are in sub - function. #}
{% block footer %}
    {# These codes will take `footer` block from whatever this template     extends from. #}
  {{super()}}
{% endblock %}

• There is macros as well in Jinja2.
• Macros is like a function but for the templating engine.
• Here is an example of macros in Jinja2.

• Here is an example of using built - in filter as well as to make custom filter.

• Here is the screenshot of the tutorial.

• Here is all kind of expression that can be used within Jinja2.

• Here is all documentation available for Jinja2, http://jinja.pocoo.org/docs/2.9/.