angle-up arrow-clockwise arrow-counterclockwise arrow-down-up arrow-left at calendar card-list chat check envelope folder house info-circle pencil people person person-plus phone plus question-circle search tag trash x
7 August 2019 Updated 30 August 2019 by Peter
post main image
With a single language there is not really a problem, we just forget about the rest of the world and build our single language Flask application. We start getting a headache when the website must support multiple languages. What exactly is a website supporting multiple languages? How many languages will be supported, and which languages? For English there are for example en-GB and en-US. Which parts ...
Read more
29 July 2019 Updated 29 August 2019 by Peter
post main image
Performance is a never ending story. At a certain moment I noticed that putting the home page on the screen took some 370 milliseconds using the Flask development server with debug messages shown. That seemed far too long! How did I notice this? Because at the bottom of every page I show the time it takes to generate a page. Please note that the timings below are from a more optimized version of the ...
Read more
26 July 2019 Updated 13 August 2019 by Peter
post main image
In Flask we have the config object which can be used to specify database parameters, email parameters, etc. When we run a Flask program it first creates the application. Once the application has been created subsequent requests skip the app creation and are redirected to the blueprint views. When Flask starts, the config variables are loaded and used. Important to understand is that every visitor ...
Read more
4 July 2019 Updated 29 August 2019 by Peter
post main image
In the past I wrote a captcha in PHP to limit email newsletter sign ups, worked fine, in fact it is still in use today. You cannot really block spam registrations. There are registration robots but there are also people being paid a few bucks to flood your website with fake or troll accounts. That is the reality and we have to face it. And now there is also deeplearning that can be used to break our ...
Read more
28 June 2019 Updated 31 August 2019 by Peter
post main image
In the endless number of problems you encounter, and solve, when starting to use new technology I was facing a new one: how to send email from my Python Docker app using the ISPConfig host MTA (Mail transfer Agent). I found there are two ways to do this: Send mail from our container to port 25 of the host where the MTA is listening on Write the mail file to a directory on the host and use a script ...
Read more
24 June 2019 Updated 31 August 2019 by Peter
post main image
You will find a lot of SQLAlchemy datetime calculation examples using e.g. Python's timedelta function. Why? I do not understand this except that this is easy. But is it correct?  Assume we we want all user records or objects created two hours ago and the record / object definition is:  class User(Base): __tablename__ = 'user' id = Column(Integer, primary_key=True) created_on ...
Read more
21 June 2019 Updated 29 August 2019 by Peter
post main image
Building on the previous post 'Flask, Jinja2 and SLQAlchemy many-to-many relationship with conditions' I looked for a way to dynamically add filter conditions and if possible also find a solution for the soft delete pattern. Soft delete is not deleting records from a table but instead marking them as deleted. This means that every table must have a deleted flag and all queries must exclude records ...
Read more
17 June 2019 Updated 31 August 2019 by Peter
post main image
Disclaimer: This my first SQLAlchemy project so I am not experienced and may make wrong statements in this post. While working on my first Flask / SQLAchemy project (I do not use Flask-SQLAlchemy) I hit a very high and thick wall. To explain this, consider you have a blog with posts and tags. There is a many-to-many relationship between posts and tags: a post can have many tags and a tag can have ...
Read more
1 June 2019 Updated 29 August 2019 by Peter
post main image
For this blog I wanted the blog post page to have three 'columns'. Why did I quote the word columns? Because what is a column on a large screen can be a row on a mobile device. Bootstrap uses containers, rows and columns. And of course, a Bootstrap column can show on the screen as a column or a row. Help! When designing a layout we must not think about columns but about screen elements and how we ...
Read more
10 March 2019 Updated 30 August 2019 by Peter
post main image
When using docker we want the size of the docker image to be minimal. Why? Many reasons. Memory footprint is one especially when running many Python Flask websites on an ISPConfig3 server.  Fortunately, from docker 17.05 we can use multistage builds. Using this we reduce our image size from 376MB to 211MB! Below are two images we can use: > docker images python 3.6-alpine 1837080c5e87 5 ...
Read more
9 March 2019 Updated 28 August 2019 by Peter
post main image
By default Alembic does not change the length of string fields, I noticed this after changing a string field from: description = Column(String(150), server_default='') to: description = Column(String(250), server_default='') No changes were made. It appears that column type change detection is off by default, so you can test it first, and can be turned on by adding 'compare_type=True' to the context. ...
Read more
13 February 2019 Updated 31 August 2019 by Peter
post main image
This is a post showing how to run a Flask app on ISPConfig3. Why? I have a VPS on the internet running Debian and ISPConfig3. It is running static sites and PHP sites. But now I also want to run my Flask python apps here. This way I can use the domain management I am used to and do not need an extra server for Python apps. This solution uses Docker to run the Flask app, printing 'Hello world', and ...
Read more