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Inject dependencies via environment variables

Project description

depenv

Depenv varies Python classes at runtime based on environment variables. For example:

import depenv

class Bird(depenv.Injectable):
  def speak(self):
    return "chirp"

class Duck(Bird):
  def speak(self):
    return "quack"

Without any environment variables:

>>> Bird().speak()
"chirp"
>>> isinstance(Bird(), Bird)
True
>>> isinstance(Bird(), Duck)
False

With DEPENV_BIRD=Duck:

>>> Bird().speak()
"quack"
>>> isinstance(Bird(), Bird)
True
>>> isinstance(Bird(), Duck)
True

Depenv aims to provide the benefits of dependency injection without the boilerplate of other dependency injection frameworks.

Installation

Depenv is available on PyPi:

pip install depenv

Depenv has no external dependencies and works for all supported Python versions.

Usage

When you create a new object using a class that subclasses depenv.Injectable, Depenv will search your environment variables for a suitable class to inject. For example:

import depenv

class Bird(depenv.Injectable):
  def speak(self):
    return "chirp"

class Duck(Bird):
  def speak(self):
    return "quack"

All Depenv environment variables are prefixed with DEPENV_.

If you do not set an environment variable, Depenv will use the injectable class:

>>> Bird().speak()
"chirp"

Configuring the injected class

The simplest Depenv configuration specifies only the injectable class name and the injected class name. For example, with DEPENV_BIRD=Duck:

>>> Bird().speak()
"quack"

If your injected class exists in a different module, you can provide an absolute path. For example, with DEPENV_BIRD=examples.birds.Duck:

>>> Bird().speak()
"quack"

Configuring the injectable class

If your injectable class shares a name with another injectable class, you can disambiguate by including a module. For example:

  • DEPENV_BIRD will match any injectable class named Bird (case insensitive) in any module.
  • DEPENV_Bird will match any injectable class named Bird (case sensitive) in any module.
  • DEPENV_EXAMPLES_BIRDS_BIRD will match any injectable class named Bird (case insensitive) in the examples.birds (case insensitive) module.
  • DEPENV_examples_birds_Bird will match the injectable class named Bird (case sensitive) in the examples.birds (case sensitive) module.

Because . is in invalid charcter in environment variable names, Depenv uses _ in its place. Consequently, all of the following will matchthe environment variable DEPENV_examples_birds_Bird:

  • examples.birds.Bird
  • examples.birds_Bird
  • examples_birds.Bird
  • examples_birds_Bird

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