HTML if else condition for printing items in list-CodePudding

I'm making a website with flask, and I pass in a list. My .html file has this code:

{$ for file in list %}
 <div> 
 <img ... > </img>
</div>
{% endfor %}

Now if list.length == 0 I want it to just do something like

<h2> Error </h2>

instead. How do I make an if statement to check if the list is empty, and if it is then I print error on the website, if it is not, I print the images in the list. I tried to put:

<script>
 if(list.length==0){
<h2>Error</h2>
}
else{
"the for loop stuff"
}
</script>

but this does not work. THanks

CodePudding user response：

In Flask with Jinja2 as a template engine, the if-else syntax requires you to write the following statement

{% if mylist.length == 0 %}
    <div>error</div>
{% else %}
    <!-- loop -->
{% endif %}

Note: Since list is a Python keyword i suggest you to use another name for your list in order to avoid possible conflicts.

CodePudding user response：

In this pythonprogramming page about flask 7, you will find some example code and a video.

I have noted that the example does not use any <script> tag and therefore decided to post my answer to share this learning resource (not sure if it helps).

You can see the syntax for if-else statements below (unfortunately not exactly matching your example):

{% for post in posts %}
    <h3> {{ post.title }}</h3>
    <p>{{ post.body }}</p>
 
    {% if author %}
    <span style="font-size:0.5em;color:yellowgreen">{{ post.author }} </span>
    {% endif %}
    
    {% if date %}
    <span style="font-size:0.5em;color:yellowgreen">{{ post.date }}</span>
    {% endif %}
 
{% endfor %}

The comparison operator is almost the same everywhere as you can see in both the Python and Jinja references. Therefore, the equivalent for your code would be:

{% if list.length == 0 %}
...
{% endif %}