what are the differences between import and extends in Flask?

Question

I am reading 《Flask web development》. in Example 4-3，

{% extends "base.html" %}
{% import "bootstrap/wtf.html" as wtf %}

I'd like to know: What are the differences between extends and import?(I think they are quite similar in usage.) In which situation,I will use extends or import?

Answer 1

When you extend another template the template controls you (the called controls the caller) - only named blocks in the "parent" template will be rendered:

{% extends "base.html" %}
{% block main_content %}
Only shows up if there is a block called main_content
in base.html.
{% endblock main_content%}

On the other hand an import simply binds the template to a name in your template's scope, and you control when and where to call it (the caller controls the called):

{% import "bootstrap/wtf.html" as wtf %}
Some of your own template code with {{ wtf.calls() }} where it makes sense.

Answer 2

There is a difference. {% extends parent.html %} allows you to render parent.html and also override {% block %}'s defined in it while {% import %} just allows you to access template variables.

So example template is extends base.html and imports variables from bootstrap/wtf.html. Think about it like python's class inheritance and import statement.