Using the Python interpreter

Learning outcomes

• Practice using the documentation of your HPC cluster
• To be able to login to your HPC cluster
• To be able to load Python
• To be able to run a minimal Python program

For teachers

Teaching goals are:

• Learners have used the documentation of their HPC cluster
• Learners have used the Python interpreter
• Learners have loaded Python

Other goals are:

• Verify that learners indeed have learned how to login
• Verify that learners indeed have learned how to use the module system

Prior and feedback question:

• On an HPC cluster, what are software modules?
• On an HPC cluster, which problem do software modules solve?
• On an HPC cluster, why don't we let users install all software themselves?
• What does it mean that Python is an interpreted language?
• What is an interpreter?

Notes:

• For those that use Bianca, it may take some time to get a login node. Encourage those to try Pelle while waiting

Why software modules are important

Software modules allows users of any HPC cluster to activate their favorite software of any version. This helps to assure reproducible research.

Why the Python interpreter is important

flowchart TD
  a_letter[A letter to do something]
  employee[Employee]
  something_done[Something is done]
  a_letter --> employee --> something_done

  code[Code] 
  interpreter[Interpreter]
  machine_code[Machine code]
  code --> interpreter --> machine_code

The Python interpreter is the program that lets your Python code do something. It is at the heart of using Python: without it, you cannot do Python programming.

Exercises

Enjoy a video?

You can find a video with solutions to these exercises:

HPC Cluster	Login method	Videos
Alvis	SSH	Video
Bianca	SSH	Video
COSMOS	SSH	Video
Dardel	SSH	Video
Kebnekaise	SSH	Video
LUMI	SSH	Video
Pelle	SSH	Video
Rackham	SSH	Video
Tetralith	SSH	Video

To develop code in Python on your HPC clusters, one needs to:

• Login to that HPC cluster, to be able to work on it
• Load the Python module, to be using the right Python interpreter and environment
• Use the Python interpreter, to run Python code

Luckily, the documentation of your HPC center should allow you to do this by yourself!

These exercises will ensure you are able to run a minimal Python program.

How difficult will this exercise be?

The difficulty of these exercises depends on your HPC cluster:

HPC cluster name	Need VPN?	Need SSH keys?	Need 2FA?	Documentation	Difficulty
Alvis	Yes	No	No	Minimal	Medium
Bianca	Yes	No	Yes	Excellent	Medium
COSMOS	No	No	Yes	Good	Easy
Dardel	No	Yes	No	Minimal	Medium
LUMI	No	Yes	No	Reasonable	Medium
Kebnekaise	No	No	No	Good	Easy
Pelle	No	No	No	Excellent	Easy
Rackham	No	No	No	Excellent	Easy
Tetralith	No	No	Yes	Good	Easy

Exercise 1: remember a Zoom room

We will use breakout rooms, as this is best for learning. Ideally, each breakout room has 2 learners for the same HPC cluster. As it cannot be predicted how many learners show up per cluster, we do this dynamically.

• Remember a breakout room of your HPC cluster, from the schedule below

HPC cluster name	Main breakout room
Bem2 and Vera	Room 1
Bianca	Room 2
COSMOS and Rackham	Room 3
Dardel 1	Room 4
Dardel 2	Room 5
Tetralith 1	Room 6
Tetralith 2	Room 7
Tetralith 3	Room 8
Tetralith 4	Room 9
Tetralith 5	Room 10
Tetralith 6	Room 11
Tetralith 7	Room 12
Tetralith 8	Room 13
Tetralith 9	Room 14
Tetralith 10	Room 15
Tetralith 11	Room 16

• Go there
• Learners will be ruthlessly moved between rooms until all rooms have 2 or 3 people present

Exercise 2: login to your HPC cluster

Login to your favorite HPC cluster. This should be easy, as this is a prerequisite for this course.

Exercise 3: load the Python module

Go to the documentation of your HPC cluster and load a Python software module of the version indicated in the table below.

HPC Cluster	Python version
Alvis	3.12.3
Bianca	3.11.4
COSMOS	3.11.5
Dardel	3.12.3
Kebnekaise	3.11.3
LUMI	3.11.7
Pelle	3.13.1
Rackham	3.12.7
Tetralith	3.10.4

Answer

From the documentation of your center, searching for, for example, 'Python module', you will find information on how to load the Python module.

HPC Cluster	Documentation	Solution
Alvis	Short documentation or long documentation	module load Python/3.12.3-GCCcore-13.3.0
Bianca	Documentation	module load python/3.11.4
COSMOS	Documentation	module load GCCcore/13.2.0 Python/3.11.5
Dardel	Documentation and more documentation	module load PDC python/3.12.3
Kebnekaise	Documentation	module load GCC/12.3.0 Python/3.11.3
LUMI	Documentation	module load cray-python/3.11.7
Pelle	Documentation	module load Python/3.13.1-GCCcore-14.2.0
Rackham	Documentation	module load python/3.12.7
Tetralith	Documentation	module load Python/3.10.4-env-hpc2-gcc-2022a-eb

• means that the documentation does not clearly answer this question. You may find that you can piece it together easily enough or you may find that you cannot. You are encouraged to contact your HPC center to help them help you better

Exercise 4: start the Python interpreter

Go to the documentation of your HPC cluster and start the Python interpreter.

Answer

From the documentation of your center, searching for, for example, 'Python' or 'Python interpreter', you may find information on how to start the Python interpreter.

HPC Cluster	Documentation	Solution
Alvis		python
Bianca	Documentation	python
COSMOS		python
Dardel	Documentation	python
Kebnekaise		python
LUMI	Documentation	python
Pelle	Documentation	python
Rackham	Documentation	python
Tetralith	Documentation	python

• for this specific question means that the documentation does not answer this (or the answer is hiding in more complicated examples). You may find this an acceptable omission or you may not. You are encouraged to contact your HPC center to help them help you better

Cannot get this to work?

If there is no time to get this fixed during the course, you can also use Python on your local computer.

Exercise 5: run a 'Hello world' program

Copy-paste the following code to the Python interpreter:

print('Hello, world!')

Press enter.

How does that look like?

Answer

Your output will look similar to this:

$ python
Python 3.12.3 (main, Nov  6 2024, 18:32:19) [GCC 13.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> print('Hello, world!')
Hello, world!
>>> 

Congratulations, you've just run a 'Hello world' program