XAL is a contextual execution framework for Python. Through its contextual execution system, it makes a resource abstraction layer possible.
In Python, there are several tools to perform actions on the local system. As an example, the subprocess module makes it possible to run arbitrary shell commands. So, let’s suppose you wrote a script that echoes “Hello world!” using the shell:
import subprocess subprocess.call(['echo', u'Hello world!'])
Then what if you want to run commands on a remote machine? You can write a fabfile:
from fabric import api as fab_api @fab_api.task def hello(): fab_api.run(['echo', 'Hello world!'])
Then what if you want to run the command as an admin? With Fabric:
from fabric import api as fab_api @fab_api.task def hello(): fab_api.sudo(['echo', 'Hello world!'])
Then what if you want to run the command as a sudoer, on the local machine? Fabric doesn’t provide a wrapper for that:
from fabric import api as fab_api @fab_api.task def hello(): fab_api.local(['sudo', 'echo', 'Hello world!'])
Then what if you want to run it on a Windows machine? You’ll have to adapt the code.
Then what if you migrate to another deployment tool, such as zc.buildout or Salt? You’ll have to change the code.
Even with Fabric, we had to write 3 distinct scripts to be able to face all situations. As developers, we’d like to write only one function, then pass it parameters:
- run on local machine or on remote client;
- run as current user, as admin/root, or maybe as another user.
That’s why xal were created: write portable high-level system scripts.
There are so many commands and so many systems... it would be impossible to support them all. And even if it was, it would be made of tons of code and dependencies. That’s the first reason why XAL is a framework:
- focus on the API;
- allow plugins;
- keep framework lightweight.
Fully configurable, no global states¶
XAL is not designed to use global states. XAL registry is entirely configurable: you can change providers’ mapping, configure providers or write custom ones.
However, for convenience, XAL offers some configuration helpers, so that common use cases are covered easily.