Code Kata: Translate a decimal text to roman

A code kata is a an exercise of coding where the objective is to use simple requirements to train the coding and testing skills.You can use it to train brainstorming and analysis within the team as well.

The subjacent idea is to use the martial arts concept of kata to coding, where repetition leads to perfection.

A few tips:

  • Try to fit the analysis, coding and testing within a small range of time, like 2 hours or less.
  • Remember if it takes too long or demands a big effort, there will be no motivation to repeat it in another session.
  • Most of the exercises exist to train the TDD methodology.
  • You can find several exercises in the internet for your use, or just invent one yourself.

Translate a decimal text to roman

Imagine you have a text, or a list of texts, such as the one below, with words and numbers.
(or just write a text with words and numbers):

You want to replace all the decimal numbers with roman numbers

That said, there is also considerable cause for optimism among those who support OER. The awareness and adoption levels may be low, but they also show steady year-to-year improvements. For example, the open-licensed textbook adoption rate of 9% for 2016-17 represents a substantial increase over the rate of 5% for 2015-16. Likewise, awareness of both Creative Commons licensing and OER itself has increased each year.
OER also addresses a key concern of many faculty: the cost of materials. A majority of faculty classify cost as “Very important” for their selection of required course materials. Faculty report that their required textbooks have an average price of $97, and only 22% say that they are “Very satisfied” with that cost. It is therefore not surprising that most faculty report that not all of their students buy all the required texts for their class, with only a third saying that 90% or more of their students have purchased the required textbook.

Have a nice session!


If you implement this kata and you publish it in the internet, be kind a refer to this article. 😃

The text used in the exercise was extracted from a text file I have found in the internet. There is no special meaning to consider.

Jupyter notebook – Execute with parameters using CLI

Jupyter notebook – Execute from Command Line with parameters

The best way to execute a jupyter notebook with parameters is to use Papermill

  1. install: pip install papermill
  2. create a cell at the start of your jupyter notebook and add the tag: parameters
  3. add your variables to that cell
  1. and execute the command

papermill my-jupyter-notebook.ipynb my-output-notebook.ipynb -p project_key data-science-proj-key -p date '2021-08-01'

  • --p – the variable name and the value to be injected

More details here: papermill@github

Jupyter Notebook – Execute from Command Line

Jupyter notebook – Execute from Command Line

A typical command to execute a jupyter notebook from command line:

jupyter nbconvert --to notebook --execute mynotebook.ipynb --output output-name

  • --to notebook – the output format
  • --execute – the name of the notebook to be executed
  • --output – an optional name for the generated file

One question sometimes asked is if it is possible to pass parameters to a jupyter notebook.

  • Yes, it is possible, but you need help from papermill. See my next posts for more details.

Jupyter notebook – export to html

Jupyter notebook – Export to HTML

A typical command to export a jupyter notebook to html:

jupyter nbconvert my-notebook.ipynb --to html --no-input --no-prompt --output my-notebook-html

  • --to html – the output format
  • --no-input – without the python code
  • --no-prompt – remove the prompts from the output
  • --output – an optional name for the html generated file

How to extract an attribute from using bash

In some projects the version is written in the file using the attribute:

I usually use this version as the version to be tagged in the Sonar server, for code analysis. This way, it is easier to have metrics more accurate when checking the new code against the previous release.

How to get the version. Alue using bash:
cat | “ˆ\sversion\s=“ | cut -d’=‘ -f2

And for the definition

you should see

How to get or display the project version from maven

When I am doing quality analysis on projects, one of the things I like to use is the real version of the project in Sonar.

How to extract it from maven projects?

mvn -q -Dexec.executable=echo -Dexec.args=‘${project.version}’ --non-recursive exec:exec

If your pom.xml has something like

You should see:

How many unit tests?

There are several advantages in developing unit tests:

  • finds bugs early
  • You trust your code
  • Makes your code simpler, because you probably refactor it to make the tests easier to develop
  • It documents your code. The name of each unit test almost describes the feature
  • You will be more confident to change the existing code
  • It documents your code
  • The unit tests when running they are debugging your code
  • It makes it easier to troubleshoot production issues. You can reduce the scope of the analysis
  • It reduces costs. Code with fewer bugs reduces the costs of troubleshooting later
  • They execute faster than the other tests. You can use them as a rapid verification of the quality of our code.

Looking at all these advantages, we surely start to think we should develop as many unit tests as possible.
But the truth is, you should develop just enough unit tests.

How many unit tests are enough?

Let’s first analyse the consequences of developing unit tests:

  • Every unit test increases the coupling between your production code and the unit test. Meaning, every time you change the production code, you need to update one or several unit tests.
  • Developing unit tests takes time, not only developing but maintaining them too
  • It is very easy to start testing code that doesn’t need testing, such as the use of external frameworks. I see this a lot!
  • The unit tests, test the algorithm, not the functionality. You will prefer to use that time to develop integration tests, they cover more code with just only a few tests. Be aware they require some preparation, though (a future post)
  • Can create a lot of coupling if you use have to use a high quantity of mocks

Looking at all these advantages and disadvantages, I usually advise:

  • target a coverage around 70%, more than this starts to create a high couple between the code and the tests
  • Use an approach of risk-based testing, meaning
    • choose to test the branch in your method or unit that covers the most important functionality
    • cover the code that cannot fail because it brings costs to the company
  • Develop them at the same time as you develop the method, otherwise, the code will become complicated to test. Use a TDD-ish approach.

Pass a parameter to all JVMs in a machine at the same time


Imagine a scenario where you need to change a JVM parameter, but you can’t or is not a good solution to changing the start script of your server(s).

One of the challenges we had, when we were working with containers, was a way to change a parameter to a JVM without building the docker image again.
The application at the start time should read a JVM parameter where a _user profile_was defined.
For specific reasons we sometimes need to change this profile, for instance, to use a more controlled user where we can debug an issue. In these situations, we want to stop the container/pod, change the profile and start again, or even start a different container with a different profile.

As you know, the way to pass a JVM parameter to an application is
java -Dprofile=myValue com.some.Application appParameter1 appPaparameter2

What if I don’t have access, or is not viable to rewrite the above line?
You can add to the Environment variables of your operating system

JAVA_TOOL_OPTIONS=‘-Dvar1=value1 -Dvar2=value2’

Yes, you can add multiple values, since it is not a parameter, but an environment variable whose values will be injected into the JVM at starting time.

When the JVM starts it searches for this environment variable and uses it. You can check the output of the JVM displaying a message with the values found.


This environment variable has a different purpose, it adds its values as a prefix to the Java other values


export JDK_JAVA_OPTIONS=‘-Dparam=value @someFile

When we execute this
java @otherFile

The real execution is
java -Dparam=value @somefile @otherFile

Code complexity: Cyclomatic vs Cognitive

As the name suggests, code complexity measures how complex is your code. If you consider the number of possible paths your code produces, the measure is called cyclomatic. If you want other angle to measure the complexity, such as how difficult is to be read by a human, we call it cognitive.

Why is this measure important

If we take the following code

a graph like this one can be produced

From this graph we can deduce the number os possible paths an application can follow during its execution M=6-5+2x1, or 3. (Check the formulas below)
If you develop unit tests, you easily reach the conclusion that exists a strong correlation between the number of possible paths and the number of unit tests necessary to reach a coverage of 100% of the code!
Now, if your method, is too complex, or/and has a lot of possible paths of execution, you will need to develop and maintain a lot of unit tests, and, for sure, difficult for another person to understand and continue your work.
You want to have a low value for this metric. Usually, Sonar proposes a maximum value of 15. For any value above this one, you should consider refactoring your code.
By the way, the recommended value is 4 or 5.

Cyclomatic complexity

This measures how difficult is your code to be tested.
If you consider a graph generated from code, you can use the formula

E -> the number of edges in the graph
N -> the number of nodes in the graph
P -> the number of connected components (a method is considered a component, so in these cases P = 1)

For Java like languages another way to calculate exists

  • assign one point for the start of the method
  • Add one point for each conditional statement, such as an if
  • Add one point for each iterative statement
  • Add one point for each case or default in a switch
  • Add one point for each Boolean condition &&, ||
  • Sometimes it is added one point for each throws, throw, catch, and finally blocks, but it is advised to not use these points since Java has a very verbose code regarding exceptions

Cognitive complexity

This measures how difficult is your code to be read and understood.
There isn’t a specific formula to apply, but usually what is done is to take the regular formula for the Cyclomatic complexity and take into consideration how hard is to assess mentally the code

  • add points for catch, switch
  • Ignores the number of Boolean operator in an if, because mentally the effort is the same to read a && b and the a && b && c
  • Add points for each recursion (the Cyclomatic ignores this)
  • Increments for nested flows-break structures

Tools to measure the complexity

These are the ones I use most

Google for complexity metrics and several plugins for several languages and IDEs will be displayed.

Observer pattern

The observer pattern is one of the most used patterns when developing current web technologies.
For instance, in the interface when you change a value, such as a date, and something changes immediately in another place of the UI, it is the Observer pattern working behind the scenes.
When you make a REST API in an angular application, you register a method that will process the result after receiving the response, it is the Observer pattern.
In applications with buttons and dropdowns that affect other controls, it is again the Observer pattern.

what is the main idea of this pattern

You want to use this pattern when a component should be immediately notified when something changes its state or a specific behaviour happens.
By the way, this pattern is not the same as “publisher-subscriber”, but that’s a subject for another article.

An example

To avoid the common examples, imagine we have a class that every time a record is sent to a database a set of other classes want to know about, for instance, a logger and an audit class.
Let’s write a simple draft to understand a possible implementation.

  • We have a CustomerDao, the class responsible to send data to the database and the class that has information of utility to others classes
  • We have an interface for Subscriber to allow any class to be notified if it implements this interface
  • And we have 2 other classes to be Subscibers DatbaseLoggerObserver and DatabaseAuditObserver, to be notified from the CustomerDao every time a new Customer is inserted, but since they are decoupled from the CustomerDao they can receive from anywhere

Usually a possible flux would be
1. create the instances of the classes
2. Add the subscribers to the CustomerDao
3. Execute!

this is just a snippet to understand the pattern, a production code can and should do so much better. For instance you can extract the subscribers list and operations to add and remove them to another class, and so on

Advantages and disadvantages


  • Allows to send data to other objects without knowing them
  • If it is well implemented the objects interact in a loosely coupled way
  • Observers can be added and removed at any time without changing the code


  • Look for performance issues since each notification waits for each observer
  • What happens if an observer throws an exception?


This is a great pattern and is widely used at the code level, such as events in the interface, trigger behaviour in specific classes and methods and so on.
This pattern is not a good option if you need this behaviour at the architecture level, since it doesn’t have mechanisms regarding performance, scalability, reliability, etc. For these cases consider to use publisher-subscriber