checkenv

A modern best-practice is to store your application's configuration in environmental variables. This allows you to keep all config data outside of your repository, and store it in a standard, system-agnostic location. Modern build/deploy/development tools make it easier to manage these variables per-host, but they're still often undocumented, and can lead to bugs when missing.

This module lets you define all the environmental variables your application relies on in an env.json file. It then provides a method to check for these variables at application launch, and print a help screen if any are missing.

Inspired from the popular npm package, checkenv.

Project Status

checkenv is actively maintained again. Version 2.0.0 is a modern maintenance release that keeps the library intentionally small while refreshing the project around supported Python versions, current packaging standards, CI, and dependency security hygiene.

The current maintained line is checkenv 2.x, which supports Python 3.11 and newer and is tested in CircleCI across Python 3.11, 3.12, 3.13, and 3.14. Legacy checkenv 1.x releases remain available on PyPI for projects that still need Python 2.7 or other end-of-life Python versions; pin checkenv<2 if you are in that situation.

Maintenance now includes Ruff linting and formatting checks, package build validation, Twine validation before publish, Snyk dependency scanning, Dependabot updates, and automated PyPI publishing from tagged CircleCI builds.

Usage

First, define a JSON file called env.json in your project root (see below for the specific structure). Next, install the library using pip connected to the PyPI index:

pip install checkenv

For the maintained 2.x line, use Python 3.11 or newer. If you need Python 2.7 or older Python 3 releases, pin to checkenv<2.

Then, add the following line to the top of your project's entry file:

from checkenv import check
check()

By default, checkenv will print a pretty error message and call sys.exit() if any required variables are missing. It will also print an error message if optional variables are missing, but will not exit the process.

You can specify a filename other than env.json by setting the optional parameter filename. The library will attempt to load this file from the root path of your project. You can also specify an absolute file path.

If you would like to handle errors yourself, check takes an optional raise_exception argument which causes it to raise exceptions instead of exiting the process.

from checkenv import check
try:
  check(raise_exception=True)
except Exception as e:
  # do something with the error 'e' because the process will not exit

An exception can be one of three classes of Exceptions:

• checkenv.exceptions.CheckEnvException - thrown if any mandatory environment variables are missing; contains missing and optional properties that contain a list of environment variable names
• jsonschema.exceptions import ValidationError - thrown if the input JSON files is invalid
• OSError - thrown if the input JSON file cannot be found

You can also silence any output to stdout by setting the optional parameter no_output=True. It is recommended to use this in conjunction with raise_exception=True and handling the error yourself; otherwise, your application can fail silently because you do not realize that something is wrong with your environment variables.

Configuration

Your JSON file should define the environmental variables as keys, and either a boolean (required) as the value, or a configuration object with any of the options below.

JSON

{
  "ENVIRONMENT": {
    "description": "This defines the current environment"
  },
  "PORT": {
    "description": "This is the port the API server will run on",
    "default": 3000
  },
  "PYTHON_PATH": true,
  "DEBUG": {
    "required": false,
    "description": "If set, enables additional debug messages"
  }
}

Object Properties

• required - Defines whether or not this variable is required. By default, all variables are required, so you must explicitly set them to optional by setting this to false.
• description - Describes the variable and how it should be used. Useful for new developers setting up the project, and is printed in the error output if present.
• default - Defines the default value to use if variable is unset. Implicitly sets required to false regardless of any specified value.

Change Log

2.0.0 - Modern Python Maintenance Release

checkenv is back under active maintenance. This release keeps the public API small and familiar, but refreshes the project for the current Python ecosystem and tightens a few behaviors that were surprising in older releases.

Breaking changes:

• Dropped support for Python 2.7 and end-of-life Python 3 versions; checkenv now requires Python 3.11+
• Removed the future compatibility dependency
• Failed checks now exit with status code 1 instead of a successful exit
• Unknown object properties in env.json entries are now rejected

Maintenance and security:

• Moved packaging metadata to pyproject.toml
• Added inline type metadata for type-aware editors and downstream users
• Added Ruff linting/formatting gates, package build validation, and a supported Python version matrix in CircleCI
• Raised package test coverage to 100% and added a coverage floor to prevent regressions
• Added Dependabot configuration and security reporting policy
• Constrained Snyk-reported vulnerable transitive development dependencies above fixed versions
• Added automated PyPI publishing from tagged CircleCI builds

Bug fixes:

• Fixed default handling for falsy values such as 0 and false
• Treat explicitly empty environment variables as set

1.2.0

• Added ability for check() to throw exceptions instead of killing the running process with raise_exception=True
• Added ability to silence all output to stdout with no_output=True
• Updated documentation with the filename parameter feature that allows you to specify an input JSON file with a different name than env.json
• Updated README.md with usage instructions for these new features
• Increased code coverage to 95%+

1.1.0

• Expanded supported Python interpreter versions - checkenv now supports Python versions 2.7, 3.5, 3.6, 3.7, and 3.8.
• Refactored the code with classes - although this does not add additional functionality, the code is cleaner, easier to understand, and better documented for future improvements
• Added tests with pytest and tox
• Every pushed branch undergoes automated testing with CircleCI
• Started tracking code coverage percentage and currently hovering around ~50% (to be improved)

1.0.0

• Initial release