A sample Python project to demonstrate basic type checking concepts and best practices.

The four sample projects included correspond to each section of the PyCon 2022 "Python Types for Fun and Profit" tutorial.

1. introduction_exercises: Annotating examples of basic data structures.
2. demo_project: Getting-started demo for setting up Pyre locally in a new project.
3. gradual_typing_project: Example project for applying type checking modes and other approaches to gradually increasing type coverage.
4. typing_pattern_exercises: More detailed and advanced Python patterns to practice expressing dynamic behavior in the type system

Tutorial Handout Sheet

Tutorial Slides

Tutorial Slides (PDF)

You'll want a python 3.10 environment and watchman, along with the latest version of the pyre-check package.

If you run into trouble, an alternative way to get started is to sign up for repl.it (you can sign in through github) and use the PyrePycon2022 repl to try out Pyre on Linux in the browser.

Watchman is a file monitoring service that records when files change. It is required to run a type checker server that delivers fast, incremental results based on file updates. Without it, you will need to run a full pyre check that type checks the entire project each time and cannot use editor integration.

brew install watchman

sudo apt-get update

sudo apt-get -y watchman

How exactly to get the latest Python release varies system to system, and you may already use a solution such as conda.

We have instructions for using pyenv for this, but you're welcome to use any other approach you know.

brew install pyenv

echo '
export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/bin:$PATH"
export PATH="$PYENV_ROOT/shims:$PATH"
eval "$(pyenv init -)"
' >> ~/.profile

. ~/.profile

pyenv install 3.10.4

sudo apt-get update

sudo apt-get install -y \
    git make build-essential libssl-dev zlib1g-dev libbz2-dev \
    libreadline-dev libsqlite3-dev wget curl llvm libncurses5-dev \
    libncursesw5-dev xz-utils tk-dev libffi-dev liblzma-dev

git clone https://github.com/pyenv/pyenv.git ~/.pyenv

echo '
export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/bin:$PATH"
export PATH="$PYENV_ROOT/shims:$PATH"
eval "$(pyenv init -)"
' >> ~/.profile

. ~/.profile

pyenv install 3.10.4

We recommend using the Windows Subsystem for Linux:

• Open a windows console in administrator mode
• Run wsl --install -d Ubuntu-20.04
• Restart your computer
• When it restarts, the Ubuntu-20.04 application should open
  • Create a user. We recommend reusing the user from your windows install, but you could create a user just for pycon
  • Now, follow the Ubuntu instructions above.

From this point forward, to work with pyre you can:

• Open the Ubuntu-20.04 application
• Do any terminal actions (like running pyre) you want from that terminal session.
• In order to use native tools, like your (VSCode editor) with files here, run explorer.exe <name_of_a_directory>
  • This will open up the directory in windows explorer.
  • From there you can do things like open files in VSCode.

You can clone this repo in one of two ways:

• First fork it to your user using the "Fork" button, and then clone from that repository
• Or, if you don't care about playing with github, just clone directly: git clone https://github.com/fbsamples/python-typing-tutorial.git

Then, set it up to use Python 3.10.4:

cd python-typing-tutorial

PYENV_VERSION=3.10.4 python -m venv pyre-venv
. pyre-venv/bin/activate

pip install pyre-check

You can make sure it works by running

cd gradual_typing_project
pyre init <<< '
'
pyre

which should spit out:

+ No type errors found

See the CONTRIBUTING file for how to help out.

python-typing-tutorial is MIT licensed, as found in the LICENSE file.