python-peps/pep-0441.txt

PEP: 441
Title: Improving Python ZIP Application Support
Version: $Revision$
Last-Modified: $Date$
Author: Daniel Holth <dholth@gmail.com>
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 30 March 2013
Post-History: 30 March 2013, 1 April 2013

Improving Python ZIP Application Support
========================================

Python has had the ability to execute directories or ZIP-format
archives as scripts since version 2.6 [1]_.  When invoked with a zip
file or directory as its first argument the interpreter adds that
directory to sys.path and executes the __main__ module.  These
archives provide a great way to publish software that needs to be
distributed as a single file script but is complex enough to need to
be written as a collection of modules.

This feature is not as popular as it should be mainly because no one’s
heard of it as it wasn’t promoted as part of Python 2.6 [2]_, but also
because Windows users don’t have a file extension (other than .py) to
associate with the launcher.

This PEP proposes to fix these problems by re-publicising the feature,
defining the .pyz and .pyzw extensions as “Python ZIP Applications”
and “Windowed Python ZIP Applications”, and providing some simple
tooling to manage the format.

A New Python ZIP Application Extension
======================================

The Python 3.4 installer will associate .pyz and .pyzw “Python ZIP
Applications” with the platform launcher so they can be executed.  A
.pyz archive is a console application and a .pyzw archive is a
windowed application, indicating whether the console should appear
when running the app.

Why not use .zip or .py? Users expect a .zip file would be opened with
an archive tool, and users expect .py to contain text.  Both would be
confusing for this use case.

For UNIX users, .pyz applications should be prefixed with a #! line
pointing to the correct Python interpreter and an optional
explanation::

    #!/usr/bin/env python3
    # This is a Python application stored in a ZIP archive, created with
    # pyzaa.
    (binary contents of archive)

As background, ZIP archives are defined with a footer containing
relative offsets from the end of the file.  They remain valid when
concatenated to the end of any other file.  This feature is completely
standard and is how self-extracting ZIP archives and the bdist_wininst
installer format work.

Minimal Tooling: The pyzaa Module
=================================

This PEP also proposes including a simple application for working with
these archives: The Python Zip Application Archiver “pyzaa” (rhymes
with “huzzah” or “pizza”).  “pyzaa” can archive these files, compile
bytecode, and can write the __main__ module if it is not present.

Usage
-----

``python -m pyzaa (pack | compile)``

``python -m pyzaa pack [-o path/name] [-m module.submodule:callable] [-c] [-w]
[-p interpreter] directory``::

    ZIP the contents of directory as directory.pyz or [-w]
    directory.pyzw. Adds the executable flag to the archive.

    ``-c`` compile .pyc files and add them to the archive

    ``-p interpreter`` include #!interpreter as the first line of the archive

    ``-o path/name`` archive is written to path/name.pyz[w] instead of
    dirname. The extension is added if not specified.

    ``-m module.submodule:callable`` __main__.py is written as “import
    module.submodule; module.submodule.callable()”

    pyzaa pack will warn if the directory contains C extensions or if
    it doesn’t contain __main__.py.

``python -m pyzaa compile arcname.pyz[w]``::

    The Python files in arcname.pyz[w] are compiled and appended to the
    ZIP file.

A standard ZIP utility or Python’s zipfile module can unpack the
archives.

FAQ
---

Q. Are you sure a standard ZIP utility can handle #! at the beginning?

A. Absolutely. If it doesn't, it is a bug in your archive program.

Q. Isn’t pyzaa just a very thin wrapper over zipfile and compileall?

A. Yes.

Q. How does this compete with existing sdist/bdist formats?

A. There is some overlap, but .pyz files are especially interesting
as a way to distribute an installer.  They may also prove useful as a
way to deliver applications when users shouldn’t be asked to perform
virtualenv + “pip install”.

References
==========

.. [1]  “Allow interpreter to execute a zip file”
   (http://bugs.python.org/issue1739468)

.. [2] “Feature is not documented”
   (http://bugs.python.org/issue17359)

Copyright
=========

This document has been placed into the public domain.



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