Software Developer

Month: May 2021

Django, django_tables2 and Bootstrap Table

I was always intrigued by Django. After all, it’s slogan is “The web framework for perfectionists with deadlines”. Last year I started a project for a client who needed a web app to manage a digital printing workflow. I evaluated Django and did their tutorial (which is really well made by the way). Since the project also required lots of data processing of different data sources (CSV, XML, etc.) Python made a lot of sense. So in the end the choice was to use Django.

I needed to create several tabIes showing data from the Django models. In this post I explain how I combined django_tables2 (for the table definitions) and Bootstrap Table (for visualizing the tables and client-side table features).

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COVID-19 Montréal Dashboard

Thanks in particular to the great German podcast Das Coronavirus-Update from NDR with two fantastic virologists (Christian Drosten and Sandra Ciesek) I gained a better understanding of the pandemic and this coronavirus (SARS-CoV-2) and learned quite a lot new stuff. Maybe because of this, I felt for a while that there was a lack here (in Québec/Montréal) about how the data is presented/visualized. But I had this realization “late” (Fall 2020) and didn’t have past data so I didn’t want to start something from scratch.

One day I randomly came across a repository on GitHub of a dashboard for Montreal. Unfortunately, the website hadn’t been updated in a while so I reached out to Jeremy Moreau who created it. We had a chat and I started helping him adding the data, adjusting to new data formats and automating the data retrieval and processing. Adding the missing data from the past was possible thanks to the Wayback Machine and (for the most part) to the hard work by Jean-Paul Soucy archiving all Canada-wide data for the COVID-19 Canada Open Data Working Group.

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SEPAQ Availability Scraper

Recently, we were trying to find an available camp site on SEPAQ during the summer. We were late to the party, though, and most (interesting) sites were already booked or had single days left here and there.

Finding the remaining sites at flexible dates is actually quite cumbersome since you need to go to each camp site (and click through a calendar week by week there) or go to a single spot of a camp site to see its availability calendar. This is especially cumbersome if you are flexible in terms of the dates and the park.

Long story short, I looked at how to get the availability of the camp sites and hacked together a scraper. It recursively finds all camping spots and downloads the availability for each of them. Once they are downloaded it can parse them and filter for available spots (with minimum days and a desired date range).

You can find the code here: https://github.com/mschoettle/sepaq-availability-scraper

There’s definitely some things that could be improved but it got the job done.

Setting up msmtp

For a long time I struggled with setting up cronjobs properly. It always took a lot of trial and error. Most of the times this was due to an environment problem (or a typo). You could test your cronjob but it would also be nice to be notified whenever something goes wrong (such as your backup script failing).

I had actually seen this output in the syslog before but never really cared much about it:

(CRON) info (No MTA installed, discarding output)

cron sends an email whenever a cronjob has an output, unless of course it cannot send the email.

So I recently set up msmtp on my server(s). I started with these instructions but in the end this is how it is working for me:

  1. Install msmtp: apt install msmtp
  2. Create the config file msmtprc in /etc (you might also need one for each user who wants to send email in ~/.msmtprc)
    • I tried to use gpg for password management to avoid storing the password as plain text. However, gpg encrypted passwords can not be decrypted with cron/sendmail. If you can, use a dedicated email account for this purpose.
  3. For cron to know where to send email to you need to do one of the following:
    • specify default email in /etc/aliases
    • specify MAILTO=recipient@domain.tld in the crontab
  4. Finally, cron uses sendmail to send out emails. You could just install the msmtp-mta package. However, you then get a From header in the emails as “root (Cron Daemon) <>”. If you want to customize this, create a sendmail alias in /usr/sbin. This is especially handy if you set this up for several servers and want to see which server an email is coming from. Follow these instructions to properly set it up. Note that starting with msmtp v1.8.8 there is a configuration setting (set_from_header) for this.
msmtp configuration
# find out more about the configuration here: https://marlam.de/msmtp/msmtprc.txt
# Set default values for all following accounts.
defaults
auth           on
tls            on
tls_starttls   on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
logfile        /var/log/msmtp
aliases /etc/aliases

# server
account        server
host           mail.domain.tld
port           587
from           server@domain.tld
user           server@domain.tld
password       

# Set a default account
account default : server

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