Introduction to Parallel Programming in Python

Netherlands eScience Center

Online

April 12-13, 2021

9:00

Instructors: Johan Hidding, Djura Smits

Helpers: Hanno Spreeuw, Leon Oostrum

General Information

Python is one of most widely used languages to do scientific data analysis, visualization, and even modelling and simulation. The popularity of Python is mainly due to the two pillars of a friendly syntax together with the availability of many high-quality libraries. The flexibility that Python offers comes with a few downsides though: code typically doesn’t perform as fast as lower-level implementations in C/C++ or Fortran, and it is not trivial to parallelize Python code to work efficiently on many-core architectures. This workshop addresses both these issues, with an emphasis on being able to run Python code efficiently (in parallel) on multiple cores.

We’ll start with learning to recognize problems that are suitable for parallel processing, looking at dependency diagrams and kitchen recipes. From then on, the workshop is highly interactive, diving straight into the first parallel programs. Participants will be coding along with the instructor in the style of teaching like Software Carpentry. This workshop teaches the principles of parallel programming in Python using Dask, Numba and Snakemake. More importantly, we try to give insight in how these different methods perform and when they should be used.

Who: The course is aimed at graduate students and other researchers. You need a basic skill in Python (and preferably NumPy) to participate in this workshop.

Where: This training will take place online. The instructors will provide you with the information you will need to connect to this meeting.

When: April 12-13, 2021. Add to your Google Calendar.

Requirements: Participants must bring a laptop with a Mac, Linux, or Windows operating system (not a tablet, Chromebook, etc.) that they have administrative privileges on. They should have a few specific software packages installed (listed below).

Accessibility: We are dedicated to providing a positive and accessible learning environment for all. Please notify the instructors in advance of the workshop if you require any accommodations or if there is anything we can do to make this workshop more accessible to you.

Contact: Please email training@esciencecenter.nl for more information.


Code of Conduct

Participants are expected to follow those guidelines:


Schedule

Day 1

09:00 Welcome and icebreaker
09:15 Introduction
10:05 Break
10:15 Measuring performance
11:15 Coffee break
11:30 Parallelization using Dask Arrays
12:45 Wrap-up
13:00 END

Day 2

09:00 Welcome and icebreaker
09:15 Recap
09:30 Accelerate code using Numba
10:30 Coffee break
10:45 Parallel design patterns with Dask Bags
11:45 Tea break
12:00 Workflows with Snakemake
12:45 Post-workshop Survey
13:00 END

Syllabus

Parallel Programming in Python (day 1)

  • Recognizing parallelizable problems
  • Dependency diagrams
  • Measuring performance
  • Working with Dask Arrays
  • Threading vs. Multiprocessing
  • Reference...

Parallel Programming in Python (day 2)

  • Working with Numba
  • Parallel design patterns
  • Delayed evaluation
  • Workflows with Snakemake
  • Reference...

Setup

To participate in this workshop, you will need access to the software described below. In addition, you will need an up-to-date web browser.

We maintain a list of common issues that occur during installation as a reference for instructors that may be useful on the Configuration Problems and Solutions wiki page.

TL;DR

Next to the Zoom video conferencing client, you need the following:

Run the following if you use conda:

git clone --recurse-submodules https://github.com/escience-academy/parallel-python-workshop
cd parallel-python-workshop
conda env create -f environment.yml
conda activate parallel-python
pytest

The tests should run without error. If you managed to install everything but somehow the unit tests fail, please contact us, either through an issue on Github or a mail to training@esciencecenter.nl.

Install the videoconferencing client

If you haven't used Zoom before, go to the official website to download and install the Zoom client for your computer.

Set up your workspace

Like other Carpentries workshops, you will be learning by "coding along" with the Instructors. To do this, you will need to have both the window for the tool you will be learning about (a terminal, RStudio, your web browser, etc..) and the window for the Zoom video conference client open. In order to see both at once, we recommend using one of the following set up options:

This blog post includes detailed information on how to set up your screen to follow along during the workshop.

The Bash Shell

Bash is a commonly-used shell that gives you the power to do tasks more quickly.

  1. Download the Git for Windows installer.
  2. Run the installer and follow the steps below:
    1. Click on "Next" four times (two times if you've previously installed Git). You don't need to change anything in the Information, location, components, and start menu screens.
    2. From the dropdown menu select "Use the Nano editor by default" (NOTE: you will need to scroll up to find it) and click on "Next".
    3. On the page that says "Adjusting the name of the initial branch in new repositories", ensure that "Let Git decide" is selected. This will ensure the highest level of compatibility for our lessons.
    4. Ensure that "Git from the command line and also from 3rd-party software" is selected and click on "Next". (If you don't do this Git Bash will not work properly, requiring you to remove the Git Bash installation, re-run the installer and to select the "Git from the command line and also from 3rd-party software" option.)
    5. Ensure that "Use the native Windows Secure Channel Library" is selected and click on "Next".
    6. Ensure that "Checkout Windows-style, commit Unix-style line endings" is selected and click on "Next".
    7. Ensure that "Use Windows' default console window" is selected and click on "Next".
    8. Ensure that "Default (fast-forward or merge) is selected and click "Next"
    9. Ensure that "Git Credential Manager Core" is selected and click on "Next".
    10. Ensure that "Enable file system caching" is selected and click on "Next".
    11. Click on "Install".
    12. Click on "Finish" or "Next".
  3. If your "HOME" environment variable is not set (or you don't know what this is):
    1. Open command prompt (Open Start Menu then type cmd and press Enter)
    2. Type the following line into the command prompt window exactly as shown:

      setx HOME "%USERPROFILE%"

    3. Press Enter, you should see SUCCESS: Specified value was saved.
    4. Quit command prompt by typing exit then pressing Enter

This will provide you with both Git and Bash in the Git Bash program.

Video Tutorial

The default shell in some versions of macOS is Bash, and Bash is available in all versions, so no need to install anything. You access Bash from the Terminal (found in /Applications/Utilities). See the Git installation video tutorial for an example on how to open the Terminal. You may want to keep Terminal in your dock for this workshop.

To see if your default shell is Bash type echo $SHELL in Terminal and press the Return key. If the message printed does not end with '/bash' then your default is something else and you can run Bash by typing bash

If you want to change your default shell, see this Apple Support article and follow the instructions on "How to change your default shell".

Video Tutorial

The default shell is usually Bash and there is usually no need to install anything.

To see if your default shell is Bash type echo $SHELL in a terminal and press the Enter key. If the message printed does not end with '/bash' then your default is something else and you can run Bash by typing bash.

Git

Git is a version control system that lets you track who made changes to what when and has options for easily updating a shared or public version of your code on github.com. You will need a supported web browser.

You will need an account at github.com for parts of the Git lesson. Basic GitHub accounts are free. We encourage you to create a GitHub account if you don't have one already. Please consider what personal information you'd like to reveal. For example, you may want to review these instructions for keeping your email address private provided at GitHub.

For macOS, install Git for Mac by downloading and running the most recent "mavericks" installer from this list. Because this installer is not signed by the developer, you may have to right click (control click) on the .pkg file, click Open, and click Open on the pop up window. After installing Git, there will not be anything in your /Applications folder, as Git is a command line program. For older versions of OS X (10.5-10.8) use the most recent available installer labelled "snow-leopard" available here.

Video Tutorial

If Git is not already available on your machine you can try to install it via your distro's package manager. For Debian/Ubuntu run sudo apt-get install git and for Fedora run sudo dnf install git.

Text Editor

When you're writing code, it's nice to have a text editor that is optimized for writing code, with features like automatic color-coding of key words. The default text editor on macOS and Linux is usually set to Vim, which is not famous for being intuitive. If you accidentally find yourself stuck in it, hit the Esc key, followed by :+Q+! (colon, lower-case 'q', exclamation mark), then hitting Return to return to the shell.

nano is a basic editor and the default that instructors use in the workshop. It is installed along with Git.

nano is a basic editor and the default that instructors use in the workshop. See the Git installation video tutorial for an example on how to open nano. It should be pre-installed.

Video Tutorial

nano is a basic editor and the default that instructors use in the workshop. It should be pre-installed.

Python

Python is a popular language for research computing, and great for general-purpose programming as well. Installing all of its research packages individually can be a bit difficult, so we recommend Anaconda, an all-in-one installer.

Regardless of how you choose to install it, please make sure you install Python version 3.x (e.g., 3.6 is fine).

We will teach Python using the Jupyter Notebook, a programming environment that runs in a web browser (Jupyter Notebook will be installed by Anaconda). For this to work you will need a reasonably up-to-date browser. The current versions of the Chrome, Safari and Firefox browsers are all supported (some older browsers, including Internet Explorer version 9 and below, are not).

  1. Open https://www.anaconda.com/products/individual#download-section with your web browser.
  2. Download the Anaconda for Windows installer with Python 3. (If you are not sure which version to choose, you probably want the 64-bit Graphical Installer Anaconda3-...-Windows-x86_64.exe)
  3. Install Python 3 by running the Anaconda Installer, using all of the defaults for installation except make sure to check Add Anaconda to my PATH environment variable.

Video Tutorial

  1. Open https://www.anaconda.com/products/individual#download-section with your web browser.
  2. Download the Anaconda Installer with Python 3 for macOS (you can either use the Graphical or the Command Line Installer).
  3. Install Python 3 by running the Anaconda Installer using all of the defaults for installation.

Video Tutorial

  1. Open https://www.anaconda.com/products/individual#download-section with your web browser.
  2. Download the Anaconda Installer with Python 3 for Linux.
    (The installation requires using the shell. If you aren't comfortable doing the installation yourself stop here and request help at the workshop.)
  3. Open a terminal window and navigate to the directory where the executable is downloaded (e.g., `cd ~/Downloads`).
  4. Type
    bash Anaconda3-
    and then press Tab to autocomplete the full file name. The name of file you just downloaded should appear.
  5. Press Enter (or Return depending on your keyboard). You will follow the text-only prompts. To move through the text, press Spacebar. Type yes and press enter to approve the license. Press Enter (or Return) to approve the default location for the files. Type yes and press Enter (or Return) to prepend Anaconda to your PATH (this makes the Anaconda distribution the default Python).
  6. Close the terminal window.