What is Jython?
Jython follows closely the Python language and its reference implementation CPython, as created by Guido van Rossum. Jython 2.7 corresponds to CPython 2.7.
Jython started as JPython, created by Jim Hugunin in 1997. JPython was renamed to Jython by Barry Warsaw in 1999 with the 2.0 release. Since then, Jython 2.x releases have corresponded to equivalent CPython 2.x releases.
Is Jython the same language as Python?
Yes. Jython is an implementation of the Python language for the Java platform. Jython 2.7 implements the same language as CPython 2.7, and nearly all of the Core Python standard library modules. (CPython is the C implementation of the Python language.) Jython 2.7 uses the same regression test suite as CPython, with some minor modifications.
There are a number of differences. First, Jython programs cannot currently use CPython extension modules written in C. These modules usually have files with the extension .so, .pyd or .dll. If you want to use such a module, you should look for an equivalent written in pure Python or Java. However, it is technically feasible to support such extensions, as demonstrated by IronPython. For the next release of Jython, we plan to support the C Python Extension API.
There are a number of other differences between the two implementations that are unlikely to go away. These range from the trivial - Jython's code objects currently do not have a co_code attribute because it is not possible to directly access Java bytecode from a class, without loading the file; to the significant - Jython uses Java's true garbage collection rather than Python's reference counting scheme.
What is the current status of Jython?
Jython 3.x development is in progress.
Jython 2.7.0 was released on May 3, 2015. Jython 2.7.1 release candidates will be released soon (September 2015).
Jython 2.5.3 is the last stable release for 2.5.x; we plan to release 2.5.4 final shortly (September 2015).
Jython 2.2 was released on August 22, 2007, with 2.2.1 released on October 13, 2007.
Jython 2.1 was released on December 31, 2001
Jython 2.0 was released on January 17, 2001
How fast is Jython?
The startup time and runtime performance for Jython are largely determined by the JVM. Startup time can be mitigated by using a tool like Nailgun. Running an older release of Java 7 can be much slower, due to bytecode verification.
Jython is approximately as fast as CPython--sometimes faster, sometimes slower. Because most JVMs--certainly the fastest ones--do long running, hot code will run faster over time.
Areas that are known to be slower include the expat emulation (which is used by ElementTree), bisect, datetime, decimal, heapq, and unicodedata, since these are all currently written in Python instead of Java; in CPython, these are all written in C. Future releases of Jytho can address this situation.
If you find a specific area where Jython performance is worse than CPython, and especially if you have a patch, please file a bug at http://bugs.jython.org.
How do I learn more about Jython?
Since Jython and Python are so closely related any good python book or documentation works well. There are also many good choices available and can be found easily by using your favorite search engine and searching for Jython. Here are a few of the frequently used references:
These are good starting points for learning python but by no means a complete list:
The official Python documentation - (note this covers the 2.6 version of the language and libraries). This is currently being patched against the small changes seen in Jython. Note that class decorators, the ast module, and the namedtuple factory function from 2.6 were implemented in Jython 2.5.0.
Dive into Python is a great learning resource
for Jython specific starting points try these:
An excellent book, "Jython Essentials", by Samuele Pedroni & Noel Rappin
as the song goes, "...getting to know you.."
An excellent online course by Dave Kuhlman
Be sure to check out the references at the bottom of the online course.
These are just a sampling of what's available. There is a lot out there and it covers a wide variety of topics. This will get you started and on you way to becoming a Jython developer and when you are ready for more, it's just a few clicks away.
Can I use Jython to make apps for mobile phones?
Unfortunately not. Mobile phones only have Java ME (Micro Edition) but Jython requires Java SE (Standard Edition). There is no Jython port to ME, and there is not enough interest to make it worth the effort.
However, Jython is Free and Open Source so if you have the skills and are interested then feel free to start porting it. If you want to make apps for Android smartphones, you may be interested in SL4A.