Can Jython help here? Should I run Grails above Jython and if yes, how? Somehow I should be able to run Grails and Python script on same JVM. There are other possibilities like making REST service for Python script or some interprocess communication but lets not deal with those for now.
Jython is a JSR223 scripting language, so you should be able to follow the usual methods. (http://www.jython.org/archive/22/userguide.html#embedding-jython)
ScriptEngine engine = new ScriptEngineManager().getEngineByName("python")
engine.eval("x = 2 + 2")
It might be a non-trivial thing to get your Jython and any libraries you want to use organized on your server, but if all you need is the language and the standard libraries, you should be able to just add it as a dependency in your buildfile - it is on Maven Central (compile 'org.python:jython:2.7.1b3').
But keep in mind that many python libraries (i.e. ones that use compiled C-code) are not going to work with Jython.
So, you might need to instead use a native python installation and call it as a process (using ProcessBuilder, for example). Groovy has some nice sugar for doing this sort of thing with strings.
Process process = "python mypython.py".execute()
An internet search for things like "groovy execute shell command" will yield lots of examples. Depending on your deployment scenario, this could be tricky to set up and maintain.
During developing one of my applications, I've come to a point where I'd like to give the users a more powerful filter. Therefore, I'd like to provide a simple scripting interface to the users. The scripting language would be Python.
For obvious reasons, I'd like to tighten the scope of the language to match my particular purposes (I don't want the users to touch the server's HDD files etc.). I also don't want to write a Python interpreter myself (which would be reinventing the wheel and the "new" wheel would be rectangular in the end). However, I haven't found any suitable library or module for this purpose.
Groovy's approach with its Compilation Customizers and Compiler Configuration would be exactly what I want, does something similar exist for Python?
What you're looking for is called a "sandbox" or "restricted execution." This wiki page discusses some of the details.
In a nutshell, there have been several efforts by Python geeks and gurus to build a sandbox on top of Python but they all failed eventually.
The main reason is that Python offers so many paths to do something that the sandbox would either have to forbid common use cases (rendering a lot of the library and Python code useless) or it would have to have holes in the sandbox which would make the concept useless.
So while it looks like a good and simple idea, so far, there is no solution. AFAIK, there are no hooks in Python to tweak the byte code compiler to achieve something like Groovy Sandbox.
Related:
How can I sandbox Python in pure Python?
Is there a "safe" subset of Python for use as an embedded scripting language?
I recently started learning Python. Not yet ventured into coding.
During one of my learning sessions, i came accross the term Jython.
I googled it & got some information.
I would like to know if anyone has implemented any real-world program using Jython.
Most of the time, Jython isn't used directly to write full read-world programs, but a lot of programs actually embed Jython to use it as a scripting language.
The official Jython website gives a list of projects, some written in Jython, others using Jython for scripting:
http://wiki.python.org/jython/JythonUsers
I am writing a full application in Jython at the moment, and would highly recommend it. Having all of the Java libraries at your disposal is very handy, and the Python syntax and language features actually make using some of them easier than it is in Java (I'm mostly talking about Swing here).
Check out the chapter on GUI Applications from the Jython book. It does a lot of comparisons like 'Look at all this Java code, and now look at it reduced to Python code of half the length!'.
The only caveats I've found are:
Jython development tends to run slightly behind Python, which can be annoying if you find a cool way of doing something in Python, only to discover it's not supported in the current Jython version.
Occasionally you might have hiccups with the interface between Python and Java (I have a couple of unsolved problems here and here, although there are always workarounds for this kind of thing).
Distribution is not as simple as it could be, although once you figure out how to do it, it's fairly painless. I recommend following the method here. It essentially consists of:
Exploding jython.jar and adding your own modules into it.
Writing and compiling a small Java class that creates a Python interpreter and loads up your Python modules.
Creating an executable .jar file consisting of the jython.jar modules, your own Python modules, and the Java class.
Jython really shines for dependency injection.
You know those pesky variables you have to give your program, like
file system paths
server names
ports
Jython provides a really nice way of injecting those variables by putting them in a script. It works equally well for injecting java dependencies, as well.
WebSphere and WebLogic use it as their default scripting engine for administrative purposes.
A lot of other Oracle products ship it as part of their "oracle_commons" module (Oracle Universal Installer, Oracle HTTP Server etc). It's mostly version 2.2 being deployed though, which is a bit old and clunky.
There is a list of application that uses jython at http://wiki.python.org/jython/JythonUsers
I decided to rewrite all our Bash scripts in Python (there are not so many of them) as my first Python project. The reason for it is that although being quite fluent in Bash I feel it's somewhat archaic language and since our system is in the first stages of its developments I think switching to Python now will be the right thing to do.
Are there scripts that should always be written in Bash? For example, we have an init.d daemon script - is it OK to use Python for it?
We run CentOS.
Thanks.
It is OK in the sense that you can do it. But the scripts in /etc/init.d usually need to load config data and some functions (for example to print the nice green OK on the console) which will be hard to emulate in Python.
So try to convert those which make sense (i.e. those which contain complex logic). If you need job control (starting/stopping processes), then bash is better suited than Python.
Generally, scripts in /etc/init.d are written in the "native shell" of the OS (e.g. bash, sh, posix-sh, etc). This is especially true of scripts that will be run at the lower init levels (e.g. not every directory will be mounted in single user mode, including wherever python or the site-libraries might be installed).
Most OS's provide some "helper functions" that make writing scripts in some native shell easier. These scripts define certain return codes and messages that are required/desired when writing service scripts. On RedHat based systems, see:
/etc/init.d/functions
Beyond that, the service scripts in /etc/init.d can be written in any language (including compiled languages). The general calling syntax will need to be supported. Typically there are three arguments that should be supported: start, stop, and status. Some additional arguments might be appropriate, depending on the purpose of the scripts.
% /etc/init.d/foo (start|stop|status)
Every task has languages that are better suited for it and less so. Replacing the backtick ` quote of sh is pretty ponderous in Python as would be myriad quoting details, just to name a couple. There are likely better projects to cut your teeth on.
And all that they said above about Python being relatively heavyweight and not necessarily available when needed.
Certain scripts that I write simply involving looping over a glob in some directories, and then executing some a piped series of commands on them. This kind of thing is much more tedious in python.
I've got some experience with Bash, which I don't mind, but now that I'm doing a lot of Windows development I'm needing to do basic stuff/write basic scripts using
the Windows command-line language. For some reason said language really irritates me, so I was considering learning Python and using that instead.
Is Python suitable for such things? Moving files around, creating scripts to do things like unzipping a backup and restoring a SQL database, etc.
Python is well suited for these tasks, and I would guess much easier to develop in and debug than Windows batch files.
The question is, I think, how easy and painless it is to ensure that all the computers that you have to run these scripts on, have Python installed.
Summary
Windows: no need to think, use Python.
Unix: quick or run-it-once scripts are for Bash, serious and/or long life time scripts are for Python.
The big talk
In a Windows environment, Python is definitely the best choice since cmd is crappy and PowerShell has not really settled yet. What's more Python can run on several platform so it's a better investment. Finally, Python has a huge set of library so you will almost never hit the "god-I-can't-do-that" wall. This is not true for cmd and PowerShell.
In a Linux environment, this is a bit different. A lot of one liners are shorter, faster, more efficient and often more readable in pure Bash. But if you know your quick and dirty script is going to stay around for a while or will need to be improved, go for Python since it's far easier to maintain and extend and you will be able to do most of the task you can do with GNU tools with the standard library. And if you can't, you can still call the command-line from a Python script.
And of course you can call Python from the shell using -c option:
python -c "for line in open('/etc/fstab') : print line"
Some more literature about Python used for system administration tasks:
The IBM lab point of view.
A nice example to compare bash and python to script report.
The basics.
The must-have book.
Sure, python is a pretty good choice for those tasks (I'm sure many will recommend PowerShell instead).
Here is a fine introduction from that point of view:
http://www.redhatmagazine.com/2008/02/07/python-for-bash-scripters-a-well-kept-secret/
EDIT: About gnud's concern: http://www.portablepython.com/
Are you aware of PowerShell?
Anything is a good replacement for the Batch file system in windows. Perl, Python, Powershell are all good choices.
#BKB definitely has a valid concern. Here's a couple links you'll want to check if you run into any issues that can't be solved with the standard library:
Pywin32 is a package for working with low-level win32 APIs (advanced file system modifications, COM interfaces, etc.)
Tim Golden's Python page: he maintains a WMI wrapper package that builds off of Pywin32, but be sure to also check out his "Win32 How Do I" page for details on how to accomplish typical Windows tasks in Python.
Python is certainly well suited to that. If you're going down that road, you might also want to investigate SCons which is a build system itself built with Python. The cool thing is the build scripts are actually full-blown Python scripts themselves, so you can do anything in the build script that you could otherwise do in Python. It makes make look pretty anemic in comparison.
Upon rereading your question, I should note that SCons is more suited to building software projects than to writing system maintenance scripts. But I wouldn't hesitate to recommend Python to you in any case.
As a follow up, after some experimentation the thing I've found Python most useful for is any situation involving text manipulation (yourStringHere.replace(), regexes for more complex stuff) or testing some basic concept really quickly, which it is excellent for.
For stuff like SQL DB restore scripts I find I still usually just resort to batch files, as it's usually either something short enough that it actually takes more Python code to make the appropriate system calls or I can reuse snippets of code from other people reducing the writing time to just enough to tweak existing code to fit my needs.
As an addendum I would highly recommend IPython as a great interactive shell complete with tab completion and easy docstring access.
I've done a decent amount of scripting in both Linux/Unix and Windows environments, in Python, Perl, batch files, Bash, etc. My advice is that if it's possible, install Cygwin and use Bash (it sounds from your description like installing a scripting language or env isn't a problem?). You'll be more comfortable with that since the transition is minimal.
If that's not an option, then here's my take. Batch files are very kludgy and limited, but make a lot of sense for simple tasks like 'copy some files' or 'restart this service'. Python will be cleaner, easier to maintain, and much more powerful. However, the downside is that either you end up calling external applications from Python with subprocess, popen or similar. Otherwise, you end up writing a bunch more code to do things that are comparatively simple in batch files, like copying a folder full of files. A lot of this depends on what your scripts are doing. Text/string processing is going to be much cleaner in Python, for example.
Lastly, it's probably not an attractive alternative, but you might also consider VBScript as an alternative. I don't enjoy working with it as a language personally, but if portability is any kind of concern then it wins out by virtue of being available out of the box in any copy of Windows. Because of this I've found myself writing scripts that were unwieldy as batch files in VBScript instead, since I can't usually depend on Python or Perl or Bash being available on Windows.
Python, along with Pywin32, would be fine for Windows automation. However, VBScript or JScript used with the Windows Scripting Host works just as well, and requires nothing additional to install.
I've been using a lot of Windows Script Files lately. More powerful than batch scripts, and since it uses Windows scripting, there's nothing to install.
As much as I love python, I don't think it a good choice to replace basic windows batch scripts.
I can't see see someone having to import modules like sys, os or getopt to do basic things you can do with shell like call a program, check environment variable or an argument.
Also, in my experience, goto is much easier to understand to most sysadmins than a function call.