How do I return a list as a variable in Python and use in Jinja2?

Question

I am a very young programmer and I am trying to do something in Python but I'm stuck. I have a list of users in Couchdb (using python couchdb library & Flask framework) who have a username (which is the _id) and email. I want to use the list of email addresses in a select box in a jinja2 template.

My first problem is how to access the email addresses. If I do:

for user in db:
    doc = db[user]
    emails = doc['email']
    print options

I get:

[email protected]
[email protected]
[email protected]

So I can get my list of emails. But where my brutal inexperience is showing up is that I don't know how to then use them. The list only exists in the for loop. How do I return that list as a useable list of variables? And how do I then make that list appear in my jinja2 template in an option dropdown. I guess I need a function but I am a green programmer.

Would so appreciate help.

Answer 1

lista = [ x for x in db ] # watch out for big databases, you can run out of memory

Answer 2

# assuming you have something such as this:
class User(Document):
    email = TextField()

# you can use the .load() method of the User class
users = [User.load(db, uid) for uid in db]

# now you can do this:
for user in users:
    print user.id, user.email  

# but you're using it in flask so, in your view you can send 
# this list of users to your template using something like this:

from flask import render_template
@app.route("/users")
def show_users():
    return render_template('users.html', users=users)

Now in your users.html jinja2 template the following will output a dropdown listbox of each user's e-mail

<select>
{% for user in users %}
    <option value="{{ user.id }}">{{ user.email }}</option>
{% endfor %}
</select>

Also, are you using the Flask-CouchDB extension? It might be helpful in abstracting out some of the low level couchdb coding: http://packages.python.org/Flask-CouchDB/

Disclaimer: The code above wasn't tested, but should work fine. I don't know much about CouchDB, but I am familiar with Flask. Also, I obviously didn't include a full Flask/CouchDB application here, so bits of code are missing.

Answer 3

You pass parameters to a jinja template as a dictionary d when you call the template.renderfunction(d) function (for example). Thus, you could do:

emails = []
for user in db:
    doc = db[user]
    emails.append(doc['email'])
some_jinja_template.render({'list_of_emails' : emails})

Then in the template, you could do something like:

<ul>
{% for address in list_of_emails %}
    <li><a href="mailto:{{ address }}">Send email to {{ address }}</a></li>
{% endfor %}
</ul>

To make a list of emails, for example, or handle them however you'd like.

PS - I'm sure the code could be more elegant/more optimized with a list comprehension or whatever, but I figured I should emphasize readability for a so-called "green" programmer.