Multiple Flask applications in one package

I’m almost ready to deploy pyDimension to my live server. I mentioned previously that I’d been working on the search indexer - every time a new post is saved, I break it up into a list of words and add the post’s url to a file named for each word.

The other side of the process is taking a search string, breaking it down into words and finding all of the posts that match the terms. I even have my own PageRank algorithm:

#!python
@srch.route('/', methods=['GET', 'POST'])
def search():
    if request.method == 'POST':
        terms = get_words(request.form['search_string'])
    else:
        terms = get_words(request.args.get('s', ''))
    results = []
    for t in terms:
        indexFilename = "%s/%s" % (srch.config['SEARCH_INDEX_DIR'], t)
        if os.path.exists(indexFilename):
            indexFile = codecs.open(indexFilename, encoding='utf-8', mode='r')
            results = indexFile.read().splitlines() + results
            indexFile.close()

    result_set = set(results)

    ranked_results = []
    for r in result_set:
        ranked_results.append((results.count(r), r, os.path.split(r)[1]))

    ranked_results.sort()
    ranked_results.reverse()

    return render_template('%s/search_results.html' % srch.config['SITE_TEMPLATE'],
                       terms=" ".join(terms),
                       results=ranked_results)

This is the only part of my website that isn’t served as static HTML. I guess in theory I could create a search results page for every possible word combination, but that would be stupid.

I ran into a problem though. The main application runs on a special subdomain behind a login, separate to the main site you’re reading now. The search part though is accessed anonymously and from the main site domain.

I wasn’t sure at first how to do this with Flask - I knew that I wanted to keep everything all neatly within the same package though, as it all belongs together.

My inexperience with Python lead me to creating a .wsgi file in the static site that only imported the pydimension.search module. I thought that would be quite clever, however, it still imports the whole of the Flask app, so I just ended up with a new entrypoint to the admin application.

After briefly giving up, I realised that the app object in my package was really just an arbitrary instantiation of the Flask class. I could create a new one and just add the /search route to it.

I modified the package __init__.py file:

from flask import Flask

app = Flask(__name__)
app.config.from_pyfile('site_settings.cfg')

srch = Flask(__name__)
srch.config.from_pyfile('site_settings.cfg')

import pyDimension.system
import pyDimension.access_control
import pyDimension.views
import pyDimension.search

then I changed the decorator for the search() function as you can see above. Initially, I routed it like this: @srch.route('/search', methods=['GET', 'POST']) and started my WSGI Daemon at the root of the domain, but I found that caused mod_wsgi to handle all request to the domain and just return 404 errors for everything but /search, instead, when I configured Apache, I started the daemon at /search:

<VirtualHost *:80>
    ServerName flasktest.subdimension.co.uk

    WSGIDaemonProcess flaskTest user=flask group=www-data threads=5 home=/<redacted>/searchTest
    WSGIScriptAlias /search /<redacted>/flaskTest/searchTest.wsgi

    <Directory /<redacted>/searchTest>
        WSGIProcessGroup searchTest
        WSGIApplicationGroup %{GLOBAL}
        WSGIScriptReloading On
        Order deny,allow
        Allow from all
    </Directory>
</VirtualHost>

In the .wsgi file for the static site domain, I imported srch from pyDimension instead of app:

import sys

sys.path.append('/redacted/pyDimension')

from pyDimension import srch as application

It worked!

Posted by Mike Watts On 14 May 2012