Converting Python 3.x code into jinja2 template using groupby and itemgetter()

Question

I have sorted list of cities called sorted_cities=[Atlanta, Berlin, Bern, Calgary] that I am sorting in alpha order and would like to display on the web with ability to click on the city to get detailed information as well as select city to get notifications via e-mail. I want the output on the web look as follows:

A

 Atlanta

B  
 Berlin

 Bern

C

 Calgary

I have the following code in Python 3.x that works fine:

sorted_names=sorted(names,key=str.lower)

    print(sorted_names)

   for letter, words in groupby(sorted_names,key=itemgetter(0)):

       print(letter)
       for word in words:

           print(word)

I created this code in Jinja2 but it does not work:

{% block content %}
<div>
    <form action="cities" method="post">
    {% for group in sorted_names|groupby("letter") %}
        <li><b>{{ group.grouper }} </b></li>
        {% for word in group.list %}
            <input type="checkbox" name="city" value="{{ word }}"> <a href="/{{ word }}">{{ word }}</a><br>
        {% endfor %}
        {% endfor %}

    <input type="submit" value="Submit">
    </form>
</div>
{% endblock %}

why does it not work? are you getting errors? does not appear how you want? — wgwz, Dec 13 '15 at 16:49
I am getting the following error from jinja2: jinja2.exceptions.TemplateSyntaxError: Unexpected end of template. Jinja was looking for the following tags: 'endfor' or 'else'. The innermost block that needs to be closed is 'for'. — user3151858, Dec 13 '15 at 17:11
I am thinking that there might be problem with groupby("letter") as I don't see how python understands that it needs to take first letter of each word, while it's clear in python code. — user3151858, Dec 13 '15 at 17:56
Try to declare `grouped_names = groupby(sorted_names,key=itemgetter(0))` in view and then use `grouped_names` in template — 1844144, Dec 13 '15 at 18:17

score 1 · Accepted Answer · edited May 23 '17 at 12:04

1

Here's a quick test that gets the basic functionality you are looking for. I piggy backed off of @1844144's comment. But basically just append the groupby elements to an array on the python side and pass it through to jinja. Then in jinja I do a not so clever conditional thing with a jinja filter (Length of string in Jinja/Flask)

app.py:

from flask import Flask, render_template
from itertools import groupby
from operator import itemgetter

app = Flask(__name__)

@app.route('/')
def main():
    names = ['Atlanta','Calgary','Berlin','Austin']
    sorted_names = sorted(names, key=str.lower)
    grouped = []
    for letter, words in groupby(sorted_names,key=itemgetter(0)):
        grouped.append(letter)
        for word in words:
            grouped.append(word)
    return render_template('index.html', grouped=grouped)

if __name__ == '__main__':
    app.run(debug=True)

templates/index.html:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
{% for name in grouped %}
    {% if name|length == 1 %}
        {{name}}<br>
    {% else %}
        <a href="/"> {{name}} </a><br>
    {%endif%}
{% endfor %}
</body>
</html>

Here's how it looks in the browser:

edited May 23 '17 at 12:04

Community

1
1

answered Dec 13 '15 at 18:54

wgwz

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This works well for me. I also observed that I made some errors in jinja/html code. I have question - is it possible to entirely escape jinja and output from python to html? Specifically for loops. – user3151858 Dec 14 '15 at 14:27
I'm not sure that I understand what your asking. But @lord63's solution is pretty sweet. So I think you are asking, can you avoid using templates, is this correct? In which case, you can do `from jinja2 import Template`. You can then write stuff to the template, here's the basic example (http://jinja.pocoo.org/docs/dev/intro/#basic-api-usage). Not sure that this is what are looking for. Search around SO. And again, study @lord63's solution. It's much cleaner IMO. – wgwz Dec 14 '15 at 16:17
What I meant is that I prefer not to use jinja2 templates and output python data directly into html. I think jinja just adds complexity. Otherwise, I agree that lord63's solution is more in line with jinja spirit and solution suggested originally by 1844144 is more focused on keeping things within Python world. I prefer to stick just to Python if possible. Just a personal preference. – user3151858 Dec 14 '15 at 19:26
jinja2 is fairly pythonic imo. I think that's the idea. But I understand what you are saying. – wgwz Dec 14 '15 at 19:46
I am not disputing that. I see it easier to do everything with one tool (Python) rather than learning new tool (jinja2) each time especially if it's not the main tool. – user3151858 Dec 14 '15 at 20:02

lord63. j · Answer 2 · 2015-12-15T01:23:13.137

The default filter groupby in jinja2 need the attribute to group your items. Howerver, you give the 'letter' attribute but jinja2 can't understand it since your names list don't have such attribute.

groupby(value, attribute)

Group a sequence of objects by a common attribute.

To reuse your python code, you can register a filter to jinja2 via [template_filter](http://flask.pocoo.org/docs/dev/api/#flask.Flt’s now possible to use dotted notatask.template_filter). So, you can try this way:

from itertools import groupby
from operator import itemgetter

from flask import Flask, render_template


app = Flask(__name__)


@app.template_filter()
def groupby_letter(iterable):
    return groupby(sorted(iterable), key=itemgetter(0))


@app.route('/')
def index():
    names = ['Atlanta','Calgary','Berlin','Austin']
    return render_template('index.html', names=names)


if __name__ == '__main__':
    app.run(debug=True)

and use the filter in your template like this:

{% for key, group in names|groupby_letter %}
    <li><b>{{ key }}</b></li>
    {% for word in group %}
        <p>{{ word }}</p>
    {% endfor %}
{% endfor %}

Yet another way is that you need do something to your names if you still want to use the groupby filter. We need to build a list dicts and each dict contains a 'first_letter' key, we will use it as the group attribute when using groupby filter.

from flask import Flask, render_template


app = Flask(__name__)


@app.route('/')
def index():
    names = ['Atlanta','Calgary','Berlin','Austin']
    name_dicts = [{'first_letter': name[0], 'name': name} for name in names]
    return render_template('index.html', name_dicts=name_dicts)


if __name__ == '__main__':
    app.run(debug=True)

and use the groupby filter in your template like this:

{% for group in name_dicts|groupby('first_letter') %}
    <li><b>{{ group.grouper }}</b></li>
    {% for item in group.list %}
        <p>{{ item.name }}</p>
    {% endfor %}
{% endfor %}

Thank you for the alternative solution. – user3151858 Dec 14 '15 at 14:26 — user3151858, Dec 14 '15 at 14:26

Converting Python 3.x code into jinja2 template using groupby and itemgetter()

2 Answers2