4.6 Python

Python was introduced to the public by Guido van Rossum in 1991. It has since gathered many followers and, as with Perl, is a world of its own. If you are interested in Python, read Mark Lutz's Programming Python or Lutz, Ascher, and Willison's Learning Python (both published by O'Reilly). Python is routinely compared to Perl, since it often serves the same purposes, but because this is the subject of yet another holy war, I will not go any further. Instead, feel free to browse the main Python web site at http://www.python.org/ for more information on the world of Python. The Python package, which includes the Python interpreter and the Python libraries, is available from that web site under the terms of a composite license called the Python license, which is an approved open source license.

As with Perl, you will need a properly configured interpreter to run Python code on your target. Although the main Python distribution does not support cross-compiling, a patch has been developed to this effect by Klaus Reimer and is available from http://www.ailis.de/~k/patches/python-cross-compile.diff. Klaus also provides a very well written Python cross-compiling HOWTO at http://www.ailis.de/~k/knowledge/crosscompiling/python.php.

You can follow Klaus' instructions to build Python for your target while using the appropriate names for your target instead of the arm-linux used in the instructions. To follow the same project workspace organization that we established earlier, download and extract the Python package in the ${PRJROOT}/sysapps directory. Also, instead of building Python directly in its source directory, you can use a build-python directory, as we did with the GNU tools, since Python supports this build method. In addition, use the - -prefix=${PREFIX}/${TARGET}/usr option instead of the values provided by the HOWTO. All the Python material will thereby be installed in the ${PREFIX}/${TARGET}/usr directory. This directory can then be customized and copied onto the target's root filesystem.

There are a couple of observations to be made about the resulting package. First, you will not be able to build Python with diet libc. You will need to build Python against glibc or uClibc. This means that glibc or uClibc will have to be on your target's root filesystem. When storage space on your target is limited, I suggest you use uClibc instead of glibc. Also, if you want to build Python against uClibc, you need to patch Python using the patch posted by Manuel Novoa on August 27, 2002 on the uClibc mailing list following the announcement of uClibc 0.9.15.

Second, Python has installed many libraries in the ${PREFIX}/${TARGET}/usr/lib/python2.2 directory, and many of those are large. You may want to trim down the content of this directory by deleting the components you are unlikely to use. By itself, the dynamically linked and stripped Python interpreter is 725 KB in size.

Nevertheless, Python's size and dependencies have not stopped developers from using it. The team developing the iPAQ's Familiar distribution, for instance, includes it as part of their standard packages.

Finally, as Klaus explains, you may see some warnings and failures during the build. This is because some libraries and applications are missing on your target. The Tkinter interface to libtk.a and libtcl.a will fail to build, for instance, unless you had cross-compiled and installed Tcl/Tk for your target. This doesn't mean the Python build has failed. Rather, it is an indication that one of the Python components has not built successfully. You will still be able to install and use the Python interpreter and the modules that built properly on your target.