python-direnv 0.2.2

Loads environment variables from a direnv .envrc file.

python-direnv

Python-direnv executes a direnv .envrc file and sets its environment variables. It helps in the development of applications following the 12-factor principles. This package implements the same public API as python-dotenv.

Contrary to most related python projects, python-direnv will not read key-value pairs, but actually load then extract them from a bash subshell.

This unlocks the full functionality of bash, but comes with a price (vulnerability to shell injection). This risk is mitigated using direnv's database : if a .envrc file has not been allowed to execute with direnv allow, the subshell will not be executed and will yield a PermissionError. You are responsible for what you execute.

In cases you can avoid that risk, it is recommended to use a safer approach, see related projects.

• Getting Started
• Other Use Cases
  • Load configuration without altering the environment
  • Load .envrc files in IPython
• Differences with python-dotenv
  • Streams
  • Command-line interface
  • Variable expansion
  • direnv-values
• Development
• Related Projects

Getting Started

(This package is not yet uploaded to pypi.org, but you can install it from source).

pip install python-direnv

If your application takes its configuration from environment variables, like a 12-factor application, launching it in development is not very practical because you have to set those environment variables yourself.

To help you with that, you can add Python-direnv to your application to make it load the configuration from a .envrc file when it is present (e.g. in development) while remaining configurable via the environment:

from direnv import load_direnv

load_direnv()  # take environment variables

# Code of your application, which uses environment variables (e.g. from `os.environ` or
# `os.getenv`) as if they came from the actual environment.

By default, load_direnv doesn't override existing environment variables and looks for a .envrc file in same directory as python script or searches for it incrementally higher up.

To configure the development environment, add a bash file named .envrc in the root directory of your project:

.
├── .envrc
└── foo.py

You will probably want to add .envrc to your .gitignore, especially if it contains secrets like a password.

See the section "File format" below for more information about what you can write in a .envrc file.

Other Use Cases

Load configuration without altering the environment

The function direnv_values works more or less the same way as load_direnv, except it doesn't touch the environment, it just returns a dict with the values parsed from the .envrc file.

from direnv import direnv_values

config = direnv_values(".envrc")

This notably enables advanced configuration management:

import os
from direnv import direnv_values

config = {
    **direnv_values(".env.shared"),  # load shared development variables
    **direnv_values(".env.secret"),  # load sensitive variables
    **os.environ,  # override loaded values with environment variables
}

Load .envrc files in IPython

You can use direnv in IPython. By default, it will use find_direnv to search for a .envrc file:

%load_ext direnv
%direnv

You can also specify a path:

%direnv relative/or/absolute/path/to/.envrc

Optional flags:

• -o to override existing variables.
• -v for increased verbosity.

Differences with python-dotenv

Streams

Contrary to python-dotenv, this package doesn't implement streams via the stream argument of load_direnv and direnv_values. This behaviour is unsafe with bash subshells and doesn't allow to check if you have allowed the file to be executed. The argument still exists to maintain the API, but will return a NotImplementedError.

Command-line interface

No command-line interface is implemented.

Arguments and variable expansion

This package currently doesn't support neither interpolate nor encoding arguments, because the file is read with source and variables are expanded by default with source.

Beware, variable expansion is not working in the same way as in python-dotenv, but as standard bash. This is mainly what you would expect :

With load_direnv(override=True) or direnv_values(), the value of a variable is the first of the values defined in the following list:

• Value of that variable in the .envrc file.
• Value of that variable in the environment.
• Default value, if provided.
• Empty string.

With load_direnv(override=False), the value of a variable is the first of the values defined in the following list:

• Value of that variable in the environment.
• Value of that variable in the .envrc file.
• Default value, if provided.
• Empty string.

There's however a diverging behaviour when using POSIX expansion on an existing variable, see the test test_load_direnv_redefine_var_used_in_file_no_override for more information. This will probably continue to diverge, as I think this version makes more sense.

direnv-values

The function direnv-values doesn't record environment variables if they are set to the same return value than in the current environment. This is because the dict is constructed from a diff between starting and finishing environment in the bash subshell.

This might matter if you extract some values with direnv-values, but plan to apply them in another environment.

Development

This package is essentially implemented. I want to add proper parsing and use of the direnv configuration file.

There are a lot of options under bash that we could implement to add more options for parsing the file, that might be useful for some.

There is also a direnv export SHELL function that might be better than the current source && declare -c call it it's easy to parse.

This project is licensed under GPLv3 because it's easy for someone to create and share an unsafe version. To prevent that, I want to ensure that anyone who modifies the project is required to be open about their changes and explain them clearly.

Related Projects

• python-dotenv - Dependency and main inspiration
• Honcho - For managing Procfile-based applications.
• django-dotenv
• django-environ
• django-environ-2
• django-configuration
• dump-env
• environs
• dynaconf
• parse_it
• python-decouple