Packaging Python programs as runnable ZIP files

One feature in recent versions of Python I hadn’t played around with until recently is the ability to package up a multi-module program into a ZIP file that can be run directly by the Python interpreter.  I didn’t find much information about it, so I thought I’d describe what’s necessary here.

Python has had the ability to add ZIP files to the module search path since PEP 273 was implemented in Python 2.3.  That can let you package up most of your program into a single file, but doesn’t help with the main entry point.

Things improved a bit when PEP 338 was implemented in Python 2.4, which allows any module that can be located on the Python search path can be executed as a script.  So if you have a ZIP file foo.zip containing a module foo.py, you could run it as:

PYTHONPATH=foo.zip python -m foo

This is a bit cumbersome to type though, so Python 2.6 lets you run directories and zip files directly.  So if you run

python foo.zip

It is roughly equivalent to:

PYTHONPATH=foo.zip python -m __main__

So if you place a file called __main__.py inside your ZIP file (or directory), it will be treated as the entry point to your program.  This gives us something that is as convenient to distribute and run as a single file script, but with the better maintainability of a multi-module program.

If your program has dependencies that you don’t expect to find present on the target systems, you can easily include them up in the zip file along side your program.  If you need to provide some data files along side your program, you could use the pkg_resources module from setuptools or distribute.

There are still a few warts with this set up though:

  • If your program fails, the trace back will not include lines of source code.  This is a general problem for modules loaded from zip files.
  • You can’t package extension modules into a zip file.  Of course, if you’re in a position where the target platforms are locked down tight enough that you could reliably provide compiled code that would run on them, you’d probably be better off using the platform’s package manager.
  • There is no way to tell whether a ZIP file can be executed directly with Python without inspecting its contents.  Perhaps this could be addressed by defining a new file extension to identify such files.

One Comment

  1. Posted 4 June, 2012 at 10:28 pm | Permalink

    Interesting discovery: if you just rename the .zip file to whatever.py, then it works and you can run it with “python whatever.py”…

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