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PRs welcome!

  • Consider starting a discussion to see if there's interest in what you want to do.
  • Submit PRs from feature branches on forks to the develop branch.
  • Ensure PRs pass all CI checks.
  • Maintain test coverage at 100%.


Code quality

Code style

  • Python code is formatted with Black. Configuration for Black is stored in pyproject.toml.
  • Python imports are organized automatically with isort.
    • The isort package organizes imports in three sections:
      1. Standard library
      2. Dependencies
      3. Project
    • Within each of those groups, import statements occur first, then from statements, in alphabetical order.
    • You can run isort from the command line with poetry run isort ..
    • Configuration for isort is stored in pyproject.toml.
  • Other web code (JSON, Markdown, YAML) is formatted with Prettier.

Static type checking


Pre-commit runs Git hooks. Configuration is stored in .pre-commit-config.yaml. It can run locally before each commit (hence "pre-commit"), or on different Git events like pre-push. Pre-commit is installed in the Poetry environment. To use:

# after running `poetry install`
❯ poetry shell

# install hooks that run before each commit
.venv ❯ pre-commit install

# and/or install hooks that run before each push
.venv ❯ pre-commit install --hook-type pre-push



This project uses Poetry for dependency management.

Install project with all dependencies: poetry install -E all.


  • Automatic virtual environment management: Poetry automatically manages the virtualenv for the application.
  • Automatic dependency management: rather than having to run pip freeze > requirements.txt, Poetry automatically manages the dependency file (called pyproject.toml), and enables SemVer-level control over dependencies like npm. Poetry also manages a lockfile (called poetry.lock), which is similar to package-lock.json for npm. Poetry uses this lockfile to automatically track specific versions and hashes for every dependency.
  • Dependency resolution: Poetry will automatically resolve any dependency version conflicts. pip did not have dependency resolution until the end of 2020.
  • Dependency separation: Poetry can maintain separate lists of dependencies for development and production in the pyproject.toml. Production installs can skip development dependencies for speed.
  • Builds: Poetry has features for easily building the project into a Python package.


The recommended installation method is through the Poetry custom installer, which vendorizes dependencies into an isolated environment, and allows you to update Poetry with poetry self update.

You can also install Poetry however you prefer to install your user Python packages (pipx install poetry, pip install --user poetry, etc). Use the standard update methods with these tools (pipx upgrade poetry, pip install --user --upgrade poetry, etc).

Key commands

# Basic usage:
poetry install  # create virtual environment and install dependencies
poetry show --tree  # list installed packages
poetry add PACKAGE@VERSION # add package production dependencies
poetry add PACKAGE@VERSION --dev # add package to development dependencies
poetry update  # update dependencies (not available with standard tools)
poetry version  # list or update version of this package
poetry shell  # activate the virtual environment, like source venv/bin/activate
poetry run COMMAND  # run a command within the virtual environment
poetry env info  #
poetry config true  # install virtualenvs into .venv
poetry export -f requirements.txt > requirements.txt --dev  # export deps

Testing with pytest

Integration tests will be skipped if cloud credentials are not present. Running integration tests locally will take some additional setup.

Make buckets on each supported cloud platform

Upload objects to each bucket

Upload an object to each bucket named .env.testing.

The file should have this content:

# .env
# comment
INLINE_COMMENT=no_comment  # inline comment
JSON_EXAMPLE='{"array": [1, 2, 3], "exponent": 2.99e8, "number": 123}'
QUOTES_AND_WHITESPACE='text and spaces'
OBJECT_STORAGE_VARIABLE='DUDE!!! This variable came from object storage!'

Generate credentials for each supported cloud platform

There are three sets of credentials needed:

  1. AWS temporary credentials
  2. AWS static credentials
  3. Backblaze static credentials

The object storage docs have general info on generating the static credentials.

For AWS static credentials, create a non-admin user. The user will need an IAM policy like the following. This project doesn't do any listing or deleting at this time, so those parts can be omitted if you're going for least privilege.

    "Version": "2012-10-17",
    "Statement": [
            "Effect": "Allow",
            "Action": ["s3:ListBucket"],
            "Resource": ["arn:aws:s3:::<AWS_S3_BUCKET_NAME>"]
            "Effect": "Allow",
            "Action": ["s3:PutObject", "s3:GetObject", "s3:DeleteObject"],
            "Resource": ["arn:aws:s3:::<AWS_S3_BUCKET_NAME>/*"]

After attaching the IAM policy to the non-admin user, generate an access key for the non-admin user, set up an AWS CLI profile named fastenv, and configure it with the access key for the non-admin user. AWS static credentials are now ready.

AWS temporary credentials work a little differently. Create an IAM role, with a resource-based policy called a "role trust policy." The role trust policy would look like this (<AWS_IAM_USERNAME> is the IAM user that owns the static credentials, not your admin username):

    "Version": "2012-10-17",
    "Statement": [
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::<AWS_ACCOUNT_ID>:user/<AWS_IAM_USERNAME>"
            "Action": ["sts:AssumeRole", "sts:TagSession"]

Attach the identity-based policy you created for the IAM user to the role as well.

The end result is that the IAM user can assume the IAM role and obtain temporary credentials. The temporary credentials have the same IAM policy as the regular access key, so tests can be parametrized accordingly.

Run all the tests

Once you're finally done with all that, maybe go out for a walk or something.

Then come back, and run these magic words:

# set the required input variables
# leading space to avoid storing secret key in shell history
# set `HISTCONTROL=ignoreboth` for Bash or `setopt histignorespace` for Zsh

# get AWS account ID from STS (replace fx with jq or other JSON parser as needed)
AWS_ACCOUNT_ID=$(aws sts get-caller-identity | fx .Account)

# assume the IAM role to get temporary credentials
  aws sts assume-role \
  --role-arn arn:aws:iam::$AWS_ACCOUNT_ID:role/$AWS_IAM_ROLE_NAME \
  --role-session-name fastenv-testing-local-aws-cli \
  --profile fastenv

# run all tests by providing the necessary input variables
AWS_IAM_ACCESS_KEY_FASTENV=$(aws configure get fastenv.aws_access_key_id) \
  AWS_IAM_ACCESS_KEY_SESSION=$(echo $ASSUMED_ROLE | fx .Credentials.AccessKeyId) \
  AWS_IAM_SECRET_KEY_SESSION=$(echo $ASSUMED_ROLE | fx .Credentials.SecretAccessKey) \
  AWS_IAM_SECRET_KEY_FASTENV=$(aws configure get fastenv.aws_secret_access_key) \
  AWS_IAM_SESSION_TOKEN=$(echo $ASSUMED_ROLE | fx .Credentials.SessionToken) \
  pytest --cov-report=html --durations=0 --durations-min=0.5

GitHub Actions workflows

GitHub Actions is a continuous integration/continuous deployment (CI/CD) service that runs on GitHub repos. It replaces other services like Travis CI. Actions are grouped into workflows and stored in .github/workflows. See Getting the Gist of GitHub Actions for more info.

GitHub Actions and AWS

Static credentials

As explained in the section on generating credentials for local testing, a non-admin IAM user must be created in order to allow GitHub Actions to access AWS when using static credentials. The IAM user for this repo was created following IAM best practices. In AWS, there is a GitHubActions IAM group, with a fastenv IAM user (one user per repo). The fastenv user has an IAM policy attached specifying its permissions.

On GitHub, the fastenv user access key is stored in GitHub Secrets.

The bucket host is stored in GitHub Secrets in the "virtual-hosted-style" format (<bucketname>.s3.<region>

Temporary credentials

In addition to the static access key, GitHub Actions also retrieves temporary security credentials from AWS using OpenID Connect (OIDC). See the GitHub docs for further info.

The OIDC infrastructure is provisioned with Terraform, using a similar approach to the example in br3ndonland/terraform-examples.

GitHub Actions and Backblaze B2

A B2 application key is stored in GitHub Secrets, along with the corresponding bucket host in "virtual-hosted-style" format (<bucket-name>.s3.<region-name>

See the Backblaze B2 S3-compatible API docs for further info.


  • The default branch is develop.
  • PRs should be merged into develop. Head branches are deleted automatically after PRs are merged.
  • The only merges to main should be fast-forward merges from develop.
  • Branch protection is enabled on develop and main.
    • develop:
      • Require signed commits
      • Include administrators
      • Allow force pushes
    • main:
      • Require signed commits
      • Include administrators
      • Do not allow force pushes
      • Require status checks to pass before merging (commits must have previously been pushed to develop and passed all checks)
  • To create a release:
    • Bump the version number in pyproject.toml with poetry version and commit the changes to develop.
    • Push to develop and verify all CI checks pass.
    • Fast-forward merge to main, push, and verify all CI checks pass.
    • Create an annotated and signed Git tag
      • Follow SemVer guidelines when choosing a version number.
      • List PRs and commits in the tag message:
        git log --pretty=format:"- %s (%h)" \
          "$(git describe --abbrev=0 --tags)"..HEAD
      • Omit the leading v (use 1.0.0 instead of v1.0.0)
      • Example: git tag -a -s 1.0.0
    • Push the tag. GitHub Actions and Poetry will build the Python package and publish to PyPI.