Tuesday, November 20, 2012

Python For Android (Py4A)

A better solution for cross-compiling Python for Android is to use the Py4A project which is made to be used together with SL4A (Scripting Layer For Android). If you are only interested in the Python interpreter and the runtime Python library, you can also use it standalone.
Get a local copy of the source code using  the following command:

   $ hg clone https://code.google.com/p/python-for-android/

Just focus on the python-build subdirectory and make sure the  python-build/python-src subdirectory is not present (remove it if it came with the Mercurial repository, or else the compilation will fail).
Set up your environment so that the python-for-android build script can pick up the ndk-build script from the Android NDK:

  $ export ANDROID_NDK_ROOT=/home/<your-directory>/android-ndk-r8
  $ export PATH=$ANDROID_NDK_ROOT:$PATH

Finally build Python for Android by issuing the following command:

  $ cd python-for-android/python-build
  $ rm -rf python-src
  $ bash build.sh

Note that on my Ubuntu 12.04 machine I had initially the following compilation error:

Traceback (most recent call last):
  File "build.py", line 161, in <module>
    os.path.join(pwd, 'output.temp', 'usr'))
  File "build.py", line 89, in zipup
    zip_file = zipfile.ZipFile(out_path, 'w', compression=zipfile.ZIP_DEFLATED)
  File "/home/danilo/python-for-android/python-build/host/lib/python2.6/zipfile.py", line 660, in __init__
    "Compression requires the (missing) zlib module"
RuntimeError: Compression requires the (missing) zlib module


I identified the problem in having the zlib library in my system installed under /lib/x86_64-linux-gnu/ instead of one of the traditional lib directories covered by the Python setup.py script. Also on my system I only had libz.so.1 and not libz.so. So to fix both problems I just created a symlink in the standard /usr/lib directory as follows:

  $ cd /usr/lib
  $ sudo ln -s /lib/x86_64-linux-gnu/libz.so.1 libz.so

With this fix the build.sh script was able to successfully build the zlib module for the host environment and create the following zipped files:

  • python_extras_r14.zip
  • python-lib_r16.zip
  • python_r16.zip
  • python_scripts_r13.zip

Of these I only used the python_r16.zip which contains the stripped python interpreter and the runtime libraries, and the python-lib_r16.zip which contains the include header files such as Python.h that can be used to compile Python bindings at development time.


3 comments:

  1. Hi, great post!,
    Im running the bash build.sh script, but im getting ( line 81: ndk-build: command not found) , i think this is a PATH variable problem, but i have set my variables. Im trying on a linux ubuntu12.04LTS VM. ... any ideas?

    kind regards, Leon.

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    Replies
    1. Forgot to mention i'm using NDK r9b.

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    2. Leon,
      I only tried the above procedure with NDK up to r9 and things works correctly. Are you sure you are exporting the PATH correctly? Try to run "type ndk-build" from the command line: if the shell doesn't find the tool then neither build.sh will. Make sure you do an export PATH after setting it to the location where you installed the NDK.

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