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A package for automatic generation of virtualenvs

Project description

Envbuilder is a system for automatically building virtualenvs in Python. To do this, it uses a .env config file to define parcels, which are individual pieces of Python software to be checked out and installed into the virtualenv.

It is mainly tested under Linux, but it should work under any platform that supports unix-y commands (including cygwin). In fact, you might even be able to make one config file work on both Windows and *nix if you’re careful.

Installing

To install envbuilder, you have two options: installing from git or installing from pypi. If you would like to install via git, use the following set of commands:

git clone git://github.com/jasonbaker/envbuilder.git
cd envbuilder
python setup.py install
# if you plan on making changes to envbuilder, use this command:
python setup.py develop

If you would like to install from pypi, you should use pip:

pip install envbuilder

The .env file

The .env’s file format is similar to the .ini file format, but there are some major differences. The best way to illustrate this is with an example. The following will make a virtualenv with envbuilder installed. There’s probably not any good reason to do this other than to provide an easy example for the README:

[project]
parcels = 'envbuilder', # Note the comma

    [[DEFAULT]]
    git_checkout = 'git clone $url'
    python = '$PWD/bin/python'

    [[envbuilder]]
    name = 'envbuilder'
    url = 'git://github.com/jasonbaker/envbuilder.git'
    setup = '$python setup.py develop'
    checkout = '$git_checkout'

The sections

project

This section is the top-level section. It has two possible options:

  • parcels - These are the parcels to be installed in the order they are to be installed. This is a list delimited by commas.
  • requires - This is a list of packages that will be easy_installed into the virtualenv.

DEFAULT

In this particular example, this particular section is probably not very meaningful. However, when using multiple parcels, it is useful to define default values to be used in each section. Note that these values are currently only used in string interpolation. There is no “inheritance” concept.

envbuilder

Here’s where we actually define a parcel. There are currently only two options that need to be defined: setup and checkout.

These are the shell commands that are run when you use envbuilder setup and envbuilder checkout (respectively).

String Interpolation

You’ll notice that in this example, we use something called string interpolation. Every part that begins with a $ is defined elsewhere. The order that it uses to check is the following:

  1. The current section.
  2. The DEFAULT subsection of the project section.
  3. The project section.
  4. The system’s environment variables

To run this, copy the .env file to where you want to build the project and run the following commands (the output only shows the shell commands, but the output is left out for brevity’s sake):

envbuilder co
--> git clone git://github.com/jasonbaker/envbuilder.git

envbuilder setup
--> virtualenv --no-site-packages .
--> /home/jason/src/envbuilder-src/bin/python setup.py develop
(From: /home/jason/src/envbuilder-src/envbuilder)

As you can see, the setup command is executed from within the checked out envbuilder directory (which is why the $cwd variable is required). You can also see that the checkout command was translated in the following steps:

  1. $git_checkout
  2. git clone $url
  3. git clone git://github.com/jasonbaker/envbuilder.git

Custom Commands

Now let’s add a custom command to this. Suppose we want to write a command that can give us the current status of our checked-out git repository. The finished .env file will look like this:

[project]
parcels = 'envbuilder', # Note the comma

    [[DEFAULT]]
    git_checkout = 'git clone $url'
    cwd = '/home/jason/src/envbuilder-src'
    python = '$cwd/bin/python'

    [[envbuilder]]
    name = 'envbuilder'
    url = 'git://github.com/jasonbaker/envbuilder.git'
    setup = '$python setup.py develop'
    checkout = '$git_checkout'

[commands]
    [[ status ]]
    required = True
    default = 'git status'
    working_dir = '$$PARCEL_WD'
    help = 'Check the status of all checked-out parcels'

This works much like envbuilder’s built in commands. Each parcel can override the default behavior by adding an option with the same name as the command. For instance, suppose we wanted to keep git status as the default behavior, but we wanted to make envbuilder’s output use the verbose flag. We could change the above to this:

[project]
parcels = 'envbuilder', # Note the comma

    [[DEFAULT]]
    git_checkout = 'git clone $url'
    cwd = '/home/jason/src/envbuilder-src'
    python = '$cwd/bin/python'

    [[envbuilder]]
    name = 'envbuilder'
    url = 'git://github.com/jasonbaker/envbuilder.git'
    setup = '$python setup.py develop'
    checkout = '$git_checkout'
    update = 'git status -v'

[commands]
    [[ status ]]
    required = True
    default = 'git status'
    working_dir = '$$PARCEL_WD'
    help = 'Check the status of all checked-out parcels'

A command has the following options:

  • required - If this is True and no default is set, an error will be raised if a parcel has not defined its own way to run this command
  • default - If a parcel does not have its own way of running this command, use this instead.
  • working_dir - The directory to run this within. If this is set to $$PARCEL_WD, it will be run from within the parcel’s directory.
  • help - The help text that will be given when envbuilder -h is run.

Questions

Can’t buildout do everything you’re doing?

Yes, it can (and more). I’m of the opinion that that isn’t necessarily a good thing. After all, C++ can do much more than Python. And yet, people still use Python because programming in it is much simpler.

What revision control systems do you support?

Envbuilder currently has support for svn (via an svn_checkout default option). However, you can theoretically use any revision control system that has a command-line interface.

Does envbuilder have to be used for Python?

Envbuilder was designed to be flexible enough that it could theoretically be used with other languages, but this has not yet been tried. Any saps (aka “open source developers”) willing to test this out are encouraged to do so!

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