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Welcome

This website is a multi-language CMS / Blog I build with Python, the framework Flask and SQLAlchemy. It is deployed on my ISPConfig3 (Nginx + Mariadb) server using Docker which is also used for development. Read more about this website.

Coronavirus

I investigated the deaths in The Netherlands in 2020 and looking at the data, I can only wonder why we have never had, and still do not have, a serious discussion about reopening the economy for people under 65 or, for example, people under 50. Read the findings and conclusions.

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Flask SQLAlchemy CRUD application with WTForms QuerySelectField and QuerySelectMultipleField

8 March 2021 0

Peter

post main image For a new Flask application using WTForms and SQLAlchemy, I had many relationships between tables and was looking for the easiest way to manage these tables. The most obvious choice is to use the QuerySelectField and QuerySelectMultipleField present in the wtforms-sqlalchemy package. Since I haven't used them before, I created a small application to play with. Below I show you the code (development ...

Migrating from Bootstrap 4 to Bootstrap 5

17 January 2021 0

Peter

post main image Nowadays, websites use a lot of CSS and Javascript. When you build websites, you can't test them all the time with the major browsers. Instead, you need a framework that supports all the major browsers. This framework needs to be well supported and that means only a few remain. For this site, I chose Bootstrap 4. This is not a coincidence. A few years ago I was looking for the best framework for a ...

Using Python's pyOpenSSL to verify SSL certificates downloaded from a host

17 December 2020 0

Peter

post main image While writing a script to check if websites correctly redirected to 'https:/www.' I thought to add some SSL certificate checks as well. This means I had to verify SSL certificates downloaded from a host. Is the certificate really for this website? Show me the expiration date. Is the certificate chain correct? And can we trust the certificate(s)? Initially I got stuck where many people got stuck because ...

Why your website canonical name must be 'www' (or 'app' or something else)

27 November 2020 2

Peter

post main image I know, there are many articles about this subject. But I thought it was useful to write a post about this because I did not know all the details. I assume your website can be accessed from the internet using a 'without-www' URL and a 'with-www' URL. This article is not about selecting a website URL for marketing purposes. Even if you are using a 'with-www' URL for your website, you can still communicate ...

Flask's SERVER_NAME, subdomains and 404 errors

25 November 2020 1

Peter

post main image This is a short post about Flask and the config variable SERVER_NAME. Like many developers I bumped into this at a certain moment, and I thought I share my story. Hopefully this will prevent headaches for some. My websites must be available by typing the following addresses in the browser: https://example.com = 'without-www', and, https://www.example.com = 'with-www' Whats more, for this ...

Flask, Celery, Redis and Docker

29 October 2020 0

Peter

post main image This is a post about how I use Docker and Docker-composer to develop and run my Flask website with Celery and Redis. There are many articles on the internet about this and if you are searching for them do not forget to search on Github.com. I just grabbed the bits and pieces and created my own setup. Before going into this I want to mention two other things that came up when adding Celery to Flask. The ...

Celery, Redis and the (in)famous email task example

10 October 2020 0

Peter

post main image Being able to run asynchronous tasks from your web application is in many cases a must have. One way to achieve this is to use Celery. There are many articles on the internet and some examples are given. I really liked Miguel Grinberg's posts about Celery. Very clear, thank you Miguel. But Miguel's post and most other articles are just an introduction. When you start with Celery you suddenly realize ...

Running multiple (Flask) websites with a single Docker setup

30 September 2020 0

Peter

post main image I developed one Flask website on Docker but after some time when my code became more stable I wanted to use the same setup for other websites. For one website I made a copy because it had to work yesterday. But what I really wanted was to share all the code, and some of templates. Of course every website has its own static directory, logging directory, templates, etc. The main reason for sharing is ...

Testing the Docker .dockerignore file patterns

22 September 2020 0

Peter

post main image This is a short post about something I wanted to do a long time ago and for which I finally found some time. It was not really a case of TL;DR (Too Long; didn't read), but more something like TLT;DR (Too Little Time; didn't read). As you probably know, the Docker .dockerignore file is used to prevent certain files and directories ending up in your Docker image. The Docker .dockerignore file is used ...

Using Python to get Postfix sent status for messages with a message-id

20 August 2020 0

Peter

post main image The problem: I have a website that sends emails. The emails (meta) are stored in a database before sending to the Postfix MTA. Every email the website sends has a unique message-id, something like  159766775024.77.9154479190021576437@peterspython.com. I want to check if the emails are actually sent and add this information to the email (meta) database records.  Postfix has statuses like: status=bounced ...

Functional testing a multilanguage Flask website with Pytest

25 July 2020 0

Peter

post main image Testing is hard work. It is totally different from creating or modifying functionality. I know, I also developed computer hardware, integrated circuits, hardware test systems. I wrote tests for CPUs, computer products, developed test systems. With hardware you cannot make mistakes. Mistakes may be the end of your company. Welcome to the wonderful world of software testing With software many things ...

IMAPClient and fetching body parts

26 June 2020 0

Peter

post main image I decided to temporarily shift focus from developing the software for my CMS / Blog to a smaller project. Main reason is that I hoped to learn new things about Python that are useful. I always wanted to have my own IMAP client software. Maybe my choice was also heavily influenced by some annoyance about the IMAP client Dekko2 for Ubuntu Touch, the OS of my mobile phone. I know that I should be happy ...

Must-read: Internet advertising is a company town by Trevor Jim

17 June 2020 0

Peter

post main image When searching for something on the internet you sometimes bump into an article that perfectly describes what you are already telling friends, colleagues for many years. Whether you are a publisher, a software developer, an advertising company, this Trevor Jim's article is a must-read. Here are the first lines: Internet advertising is a company town February 28, 2017 If you’ve watched a lot ...

Create your own Python custom exception classes tailored to your application

17 June 2020 0

Peter

post main image Using exceptions in Python looks easy but it is not. Probably you should study exceptions and exception handling before writing any Python code but TL;DR. There are examples on the internet, unfortunately most are very trivial. Anyway, I researched this and came up with some code I thought I share with you. Leave a comment if you have suggestions. What is an error and what is an exception, what is ...

Using icons on your Flask website and reducing 'First Contentful Paint'

29 May 2020 0

Peter

post main image There are many types of vector icons. In this post I only look at SVG-icons, and limit myself to navigation icons, sometimes also called interface icons. These icons not only look nice on websites, they also color and scale like fonts. And they are very functional. Imagine a button with the text ' Edit' in it. Replace this text with a pencil-icon and you get more space on the page while it still is ...

Sharing models, classes, Blueprints and templates between apps with Flask DispatcherMiddleWare

12 May 2020 0

Peter

post main image This site is running Flask. It uses DispatcherMiddleWare to run the frontend app and the admin app. The Flask documents state that the Flask applications in this case are entirely isolated from each other. That is true but often there is a lot of code we want to share between these apps. Things we want to share Both apps use the same database meaning we want to share the models.py file. Then we ...

Converting a SQLAlchemy MariaDb / MySQL database with Integer Primary Keys to UUID Primary Keys for a Flask website

26 April 2020 0

Peter

post main image This website uses Flask, (plain) SQLAlchemy with Alembic for migrations and MariaDb. If you do not use these, this post probably is not what you are looking for. In a previous post I wrote why many websites should use UUID Primary Keys instead of Integer Primary Keys. Even if you have a high performance website then probably only few tables are responsible for this performance. High performance websites ...

Blacklisting IP addresses on your Flask website running on Linux

16 April 2020 0

Peter

post main image You have a website and it works fine. But you notice that certain visitors are trying to mess with your forms. They come from specific IP addresses. Then there are also bots that are scanning your site. Some are necessary but others should stay away. Don't you hate this? I do. In the past I once wrote a module that returned a not so nice response very slowly, byte-by-byte, slowing down their systems. ...

Using UUIDs instead of Integer Autoincrement Primary Keys with SQLAlchemy and MariaDb

9 April 2020 0

Peter

post main image We all know the Integer Autoincrement Primary Key. Works great, much software is doing it this way. It is fast. But it also has limitations. An alternative for the Integer Autoincrement Primary Key is the UUID (Universally Unique IDentifier) Primary Key. A UUID is a 128-bit number. It can be represented by a string, for example: 05390f2b-48e8-45c7-8ae4-08272dc69122 or a hex string (the same as above ...

Eliminate repetition and improve maintenance by creating a Flask view class

24 March 2020 0

Peter

post main image Flask is hot. Everyone loves Flask. I believe the main reason is that it is so easy to start with Flask. You create a virtual environment, copy-paste a few lines of code from some example, point your browser at 127.0.0.1:5000 and there is your page. Then you hack a little with a Jinja template and you get a beautiful page. You can even run Flask on a Raspberry Pi, isn't that wonderful? My main reason ...