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Ensures specified environment variables are present during runtime

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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.


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

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

from checkenv import 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
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
  • IOError - 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.


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.


    "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


  • 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 with usage instructions for these new features
  • Increased code coverage to 95%+


  • 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)


  • Initial release

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