VirtualEnvOnDemand 5.0.1

Provides the ability for an application to install and use its runtime dependencies at import time. This allows for you to distribute python scripts and libraries without the overhead of the end-user needing to setup a virtualenv and install dependencies.

The primary means to accomplish this is to call “VirtualEnvOnDemand.enableOnDemandImporter()” which will load the hook into the importer. If an import fails, it will attempt to fetch the corrosponding module and install into current runtime.

You can also explicitly create environments and install packages into them (adding to current runtime), persistent or temporary. See “Persistent Virtualenvs” section below, and documentation for more details.

Why?

There are a multitude of uses for this. You may use it for development, share scripts and updates with others without them having to modify their virtualenv or install global packages.

You can use it for “lightweight” distributions, for example you may use third-party libs for testing, but they don’t need to be in your global setup.py “requires”, you can just import them

on-demand when you run tests. Or make up your own use!

You can simplify code deployments, by having the virtualenv created post-deploy, instead of worrying about having to deploy a virtualenv.

Basic Usage

The simpliest usage is to call VirtualEnvOnDemand.enableOnDemandImporter() which will add a hook to the “import” keyword, and if an import can’t be resolved locally, it will use pip to try to install it.

The default (controlled by deferSetup flag to enableOnDemandImporter) is to not setup the global virtualenv until needed (like when an import fails local). This allows the on demand importer to be used without penality if all requires modules are present, but still gives the robustness to install those that aren’t.

Your existing pip.conf provides the options and index url that will be searched.

This works fine and well, so long as modules have the same name as their package. When this is not the case, there are alternative functions.

To handle these using the global env created by enableOnDemandImporter, use:

MyModule = VirtualEnvOnDemand.ensureImportGlobal(‘MyModule’, ‘MyPackage’)

This will raise “ImportError” if MyModule cannot be imported and MyPackage cannot be installed, or if MyPackage does not provide MyMdoule.

There is more advanced usage, wherein you can create and stack multiple virtualenvs and handle them directory or for certain imports instead of using the global hook. See the documentation link below, and “example_explicit.py” in the source distribution for more information on that.

Creating Virtualenvs / Persistent Virtualenvs

You can use VirtualEnvOnDemand to create a virtualenv post-deployment, so you don’t have to worry about transferring a virtualenv.

Example:

if os.path.isdir(‘/tmp/MyEnv’):

myEnvInfo = VirtualEnvOnDemand.getInfoFromVirtualEnv(‘/tmp/MyEnv’)

else:

myEnv = VirtualEnvOnDemand.createEnv(packages=[‘ExamplePackage’], parentDirectory=’/tmp’, name=’MyEnv’, deleteOnClose=False)

to create an env in “/tmp” named “MyEnv”, with “ExamplePackage” installed by default.

Then, you can use:

VirtualEnvOnDemand.activateEnv(myEnv)

to activate it (allow imports from this virtualenv).

You can also use the on-demand functionality by calling:

VirtualEnvOnDemand.setGlobalVirtualEnv(myEnv, enableOnDemandImporter=True)

which will exapand the env you created as-needed, when imports fail.

Documentation

Can be found at:

https://htmlpreview.github.io/?https://raw.githubusercontent.com/kata198/VirtualEnvOnDemand/master/doc/VirtualEnvOnDemand.html