jinja2.exceptions.UndefinedError - list object has no element - displaying list in jinja2 template - Flask

Question

I have elements I get from a DB that I put in a list of lists in Python and send to a template but I get this message:

jinja2.exceptions.UndefinedError

jinja2.exceptions.UndefinedError: list object has no element [1000000001, 'TestTitle', 'TestDescription', 'static/img/uploads/lereacteur.png', datetime.datetime(2020, 5, 10, 16, 8, 46, 826822)]

[1000000001, 'TestTitle', 'TestDescription', 'static/img/uploads/lereacteur.png', datetime.datetime(2020, 5, 10, 16, 8, 46, 826822)] is the first line of the list that I want to send to the template.

The route is :

@app.route('/projects')
def projects():
    project_matrix = listOfProjects()
    print(project_matrix)
    return render_template("projects.html", projects=project_matrix)

This is the template:

{% extends 'template1.html' %}
{% block Title %} Projects {% endblock %}
{% block bodyTitle %} Projects {% endblock %}
{% block subTitle %} Test {% endblock %}
{% block body %}
<div class="projects">
  {% for project in projects %}
  <div class="project">
    <div class="projectTitle">
      {{ projects[project][1] }}
    </div>
    <div class="projectHolding">
      <div class="projectDescription">
        {{ projects[project][2] }}
      </div>
      <div class="projectImg">
        <img
          src="{{ url_for('static', filename = 'img/uploads/'+'{{projects[project][3]}}') }}"
          style="min-width: 100px; max-height: 300px;"
          alt="tether's Market Cap"
        />
      </div>
    </div>
  </div>
  {% endfor %}
</div>
{% endblock %}

This is what shows up in the terminal when I load the page:

[[1000000001, 'TestTitle', 'TestDescription', 'static/img/uploads/lereacteur.png', datetime.datetime(2020, 5, 10, 16, 8, 46, 826822)], [1000000002, 'testSecondTitle', 'testSecondDescription', 'static/img/uploads/logo-licence-miashs2.png', datetime.datetime(2020, 5, 11, 2, 4, 52, 200953)]]
127.0.0.1 - - [12/May/2020 02:15:52] "GET /projects HTTP/1.1" 500 -
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 2463, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 2449, in wsgi_app
    response = self.handle_exception(e)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1866, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 2446, in wsgi_app
    response = self.full_dispatch_request()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1951, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1820, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1949, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1935, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Users/hugo/Desktop/website/app.py", line 185, in projects
    return render_template("projects.html", projects=project_matrix)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/templating.py", line 140, in render_template
    ctx.app,
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/templating.py", line 120, in _render
    rv = template.render(context)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/jinja2/environment.py", line 1090, in render
    self.environment.handle_exception()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/jinja2/environment.py", line 832, in handle_exception
    reraise(*rewrite_traceback_stack(source=source))
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/jinja2/_compat.py", line 28, in reraise
    raise value.with_traceback(tb)
  File "/Users/hugo/Desktop/website/templates/projects.html", line 1, in top-level template code
    {% extends 'template1.html' %}
  File "/Users/hugo/Desktop/website/templates/template1.html", line 39, in top-level template code
    {% block body %} {% endblock %}
  File "/Users/hugo/Desktop/website/templates/projects.html", line 22, in block "body"
    {{ projects[project][1] }}
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/jinja2/environment.py", line 452, in getitem
    return obj[argument]
jinja2.exceptions.UndefinedError: list object has no element [1000000001, 'TestTitle', 'TestDescription', 'static/img/uploads/lereacteur.png', datetime.datetime(2020, 5, 10, 16, 8, 46, 826822)]
127.0.0.1 - - [12/May/2020 02:15:52] "GET /projects?__debugger__=yes&cmd=resource&f=style.css HTTP/1.1" 200 -
127.0.0.1 - - [12/May/2020 02:15:52] "GET /projects?__debugger__=yes&cmd=resource&f=jquery.js HTTP/1.1" 200 -
127.0.0.1 - - [12/May/2020 02:15:52] "GET /projects?__debugger__=yes&cmd=resource&f=debugger.js HTTP/1.1" 200 -
127.0.0.1 - - [12/May/2020 02:15:52] "GET /projects?__debugger__=yes&cmd=resource&f=ubuntu.ttf HTTP/1.1" 200 -
127.0.0.1 - - [12/May/2020 02:15:52] "GET /projects?__debugger__=yes&cmd=resource&f=console.png HTTP/1.1" 200 -
127.0.0.1 - - [12/May/2020 02:15:52] "GET /projects?__debugger__=yes&cmd=resource&f=console.png HTTP/1.1" 200 -

The first line tells me that the 'print(project_matrix)' sends a valid list of elements to the web page so I don't understand why the error tells me list object has no element.

Do you have any idea of where the problem comes from ?

Answer 1

You're trying to call a list index, with the list itself. You already have the list object when you enter the for loop {% for project in projects %}. So this line:

{{ projects[project][1] }}

Should be

{{ project[1] }}

Similarly for:

{{ projects[project][2] }}
{{ project[2] }}

and

src="{{ url_for('static', filename = 'img/uploads/'+'{{projects[project][3]}}') }}"
src="{{ url_for('static', filename = 'img/uploads/'+'{{project[3]}}') }}"