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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.

Recent

Connect to a service on a Docker host from a Docker container

11 August 2022 0

Peter

If you have some Docker problem and search the Internet, you will almost certainly stumble upon the question: How can I connect to localhost? What people mean is: How can I connect to a service on the Docker host from a Docker container. When I started using Docker I was also struggling with this. I am using Linux, Ubuntu, and when finally host.docker.internal was available for Linux many people thought ...

AIOHTTP: Detecting DNS timeout with custom nameservers

27 July 2022 0

Peter

When using AIOHTTP to fetch data from a web page on the internet you are probably using a timeout to limit the maximum waiting time. If you are using a domain name then the IP Address must be resolved. Without using a separate resolver you are dependent on the underlying operating system. Any errors propagate to your application. I did not want this dependency and specify the nameservers myself, ...

Flask Message Flashing: Replace Bootstrap Alerts by Toasts

25 July 2022 0

Peter

When you have a Flask application with Bootstrap, you are probably using Bootstrap Alerts to show flashed messages. I use them, and they work, but I am not really happy. By default, they do not look nice and in most cases they take a lot of space on the screen. And do you really want notifications like 'you are logged in' to be a Bootstrap Alert that must closed by the user? By adding a timeout we ...

SQLAlchemy: Using Cascade Deletes to delete related objects

16 July 2022 0

Peter

Although the documentation of SQLAlchemy ORM is very good it sometimes is confusing and lacks clear examples, but maybe this is just me. About Cascade Deletes, I find the following text from the SQLAlchemy documentation mind-blowing: The default value of the relationship 'cascade'-option is 'save-update, merge'. The typical alternative setting for this parameter is either all or more commonly 'all, ...

SQLAlchemy PostgreSQL: Add a second BigInteger Primary Key

28 May 2022 0

Peter

Suppose we use UUID Primary Keys in our project. This works fine, but there are also a few tables with millions of records. We know that SELECT and INSERT operations with UUID-based Primary Key tables can be much slower compared to Integer based Primary Key tables. What we want is for these huge tables to have only BigInteger Primary Keys and link them to other UUID Primary Key based tables, ...

Redirect on an exception in Flask using a decorator

7 May 2022 0

Peter

In a Flask application, you typically implement global exception handlers. In many cases, this is sufficient. But what if you want more control? In one project, I was connecting to an API and I wanted a number of routes that used the API to redirect to a 'start' page in case of an API error, with an appropriate message of course. I implemented this using a 'redirect_decorator' exception handler that ...

SQLAlchemy Many-To-Many: Four ways to select data

12 April 2022 0

Peter

This is a short post about Many-To-Many selection with SQLAlchemy. In the past I used the association (link) table in ORM queries, because I thought it must be fastest. This time I did a small test comparing various ways to select data. Spoiler: The association (link) table way is (of course) fastest. The model We have a Many-To-Many relationship between Orders and Products. # link table: order ...

Testing the RabbitMQ Pika publishing examples

25 March 2022 0

Peter

A lot has been written about synchronous vs asynchronous publishing with RabbitMQ, see links below, I am not going to repeat this here. As this is my first time using RabbitMQ, I wanted to try both the synchronous and asynchronous publishing versions, using examples included with Pika, the RabbitMQ (AMQP 0-9-1) client library for Python. To my surprise, the Pika asynchronous example did not detect ...

An attempt to solve Tic-Tac-Toe using Keras and LSTM

2 March 2022 0

Peter

After implementing my first Deep Learning LSTM model for a project I was thinking if Deep Learning could also solve a game. The first game that comes to mind is Tic-Tac-Toe. Then you search the internet and there appear to be many many people who had the same idea. Of course. Below I present my solution to solve Tic-Tac-Toe using Keras and LSTM (Long Short Term Memory). This is Deep Learning and not ...

LSTM multi-step hyperparameter optimization with Keras Tuner

13 February 2022 0

Peter

A previous post was about Hyperparameter optimization with Talos. I could not get this to work with my LSTM model for univariate multi-step time series forecasting, because of the 3D input, so I switched to Keras Tuner. In this post I try to predict the next period of a sine wave using the Hyperband tuning algorithm. To reduce tuner time, I reduced the number of hyperparameters that can be optimized ...

Finding the closest matching sentence from a list of sentences

6 February 2022 0

Peter

For a project I was looking for a way to match an incoming sentence with a list of fixed sentences. This is a complex subject but when searching the internet I bumped on the amazing project Sentence-Transformers. I modified one of the examples on this site to use a text file with sentences and typed some input sentences as a demo. Then I downloaded a text file from the internet 'Choosing a Cat, by ...

Automating Keras hyperparameter optimization with Talos

2 February 2022 0

Peter

In the two previous posts I showed you my first steps with Keras. I used examples found on the internet and changed the dataset into something trivial, meaning I generate the data myself and know the expected values. But I also told you that I had no idea why parameters like neurons, epochs, batch_size had these values.So what we have is not really a black box. On the outside there are also some switches ...

Predicting the next future value using Deep Learning and LSTM

30 January 2022 0

Peter

Many problems are time related. We have collected some samples and now want to use them to predict the next value. That is what this post is about. It is not about predicting many future values, that is a different topic.As a data scientist noob, I just work through some examples I found on the internet. I change the input sequence and see what happens. You might find this useful. I found the 'Machine ...

Predicting values using Deep Learning and Keras

28 January 2022 0

Peter

I have a dataset, many rows with N inputs and 1 output, and want to predict the output value for any new combination of input values. I am also a data science noob, but stories on the internet about Deep Learning suggest we can easily create some kind of black box with some neurons, nodes, in it, and then use the dataset to train the black box. After this we can feed any inputs and our black box gives ...

Python file I/O on Windows and Linux are two different things

8 December 2021 0

Peter

I have a Python program running fine on Linux. Few months ago I wanted to run this on Windows. This was the first time I used Python on Windows. Install Python app, create virtual environment, copy and run. No problems ... oh but there was a problem. My session sometimes disappeared ... WTF! I noticed the problem by repeatly hitting F5 in a very short time. Time for a thorough investigation. The ...

Create a colors class and color mapper for your application

27 November 2021 0

Peter

I was implementing some charts with Chart.js and needed to pass colors from my Flask application to the template. The graph is a line graph and the number of lines can vary. With the graph I also show a table with the (numeric) values used in the graph. The lines have different colors, I choose them from a list of colors. The table of line values has a column for each line. I want the header cell ...

Using PyInstaller and Cython to create a Python executable

6 October 2021 0

Peter

You have created a Python application and want to distribute it. You probably have it running in a Python Virtual Environment. But customers don't have this setup, some may not even have Python installed. There are several programs that can convert your Python application into a single executable file. Here I am using PyInstaller. You may also want to protect some of your code and/or speed up some ...

IMAPClient and flattening the BODYSTRUCTURE

27 September 2021 0

Peter

Application developers want to use proven solutions to create an application. Many times this works but with the IMAPClient package there are a number of things missing. The whole idea of IMAP is to get only what you request. Suppose you have an email with many attachments but you want to view or download only one of them. To be able to do this you need the 'body_number' of this attachment and then ...

Blocking unsafe resources in HTML email using BeautifulSoup

30 August 2021 0

Peter

I have created an IMAP E-Mail Reader using IMAPClient and Flask. The IMAP E-Mail Reader decodes the email into valid HTML. Then it needs to display this HTML through the browser. Works fine, so far so good. In this post I describe how I implemented an option in my IMAP E-Mail Reader to block unsafe resources in the HTML. To do this, I use BeautifulSoup and Python's Regular expression operations. Why ...

Python Multiprocessing graceful shutdown in the proper order

16 June 2021 0

Peter

For a new project I needed a deamon process that must execute many, more or less identical, operations on different resources. In this case the operation is IO bound and I solved it by using ThreadPoolExecutor. So far, so good. Next I wanted to store the results in files. Of course we use a queue to communicate between processes. The worker() process uses q.put() to add items to the queue and the ...

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Connect to a service on a Docker host from a Docker container

AIOHTTP: Detecting DNS timeout with custom nameservers

Flask Message Flashing: Replace Bootstrap Alerts by Toasts

SQLAlchemy: Using Cascade Deletes to delete related objects

SQLAlchemy PostgreSQL: Add a second BigInteger Primary Key

Redirect on an exception in Flask using a decorator

SQLAlchemy Many-To-Many: Four ways to select data

Testing the RabbitMQ Pika publishing examples

An attempt to solve Tic-Tac-Toe using Keras and LSTM

LSTM multi-step hyperparameter optimization with Keras Tuner

Finding the closest matching sentence from a list of sentences

Automating Keras hyperparameter optimization with Talos

Predicting the next future value using Deep Learning and LSTM

Predicting values using Deep Learning and Keras

Python file I/O on Windows and Linux are two different things

Create a colors class and color mapper for your application

Using PyInstaller and Cython to create a Python executable

IMAPClient and flattening the BODYSTRUCTURE

Blocking unsafe resources in HTML email using BeautifulSoup

Python Multiprocessing graceful shutdown in the proper order