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A library for deferring decorator actions

Project description

Venusian is a library which allows framework authors to defer decorator actions. Instead of taking actions when a function (or class) decorator is executed at import time, you can defer the action usually taken by the decorator until a separate “scan” phase.

See the “docs” directory of the package or the online documentation at

2.0a3 (2016-01-27)

  • Do an additional check to avoid scanning modules inserted by six for Python 3 compatibility. six assumes these modules exist in Python but some of them, like gdbm, cannot always be compiled, so don’t scan these. This hack may actually not be strictly proper as it is possible for an outer module to be ignored while an inner module is allowed by an ignore function, but we’ll not worry about that case for now.

2.0a2 (2014-07-07)

  • NOTE This will hopefully be in Venusian proper in Version 1.1; this fork is just so I can make progress with the new recursive option.
  • Add a recursive option to the .scan() method to allow the scanning of packages non-recursively (scan only).
  • Some refactoring of internals from nested functions into separate methods.

1.0 (2014-06-30)

  • Fix an issue under PyPy > 2.0 where attached decorators may not be found.
  • Drop support of Python 2.4 / 2.5 / Jython.
  • Add lift and onlyliftedfrom class decorators to allow for inheritance of venusian decorators attached to superclass methods. See the API documentation for more information.
  • Fix bug where otherwise undecorated subclass of a superclass that had venusian decorators on it would inherit its superclass’ decorations. Venusian decorators should have never been inherited implicitly. See

1.0a8 (2013-04-15)

  • Pass ignore argument along recursively to walk_packages so custom ignore functions will ignore things recursively. See
  • Don’t run tox tests under Python 2.4 anymore (tox no longer supports 2.4).

1.0a7 (2012-08-25)

  • Venusian now works on Python 3.3b2+ (importlib-based).
  • Use nose-exclude instead of relying on fragile module-scope code to ensure we don’t get errors resulting from import of fixture code during “nosetests”.
  • Bug fix: no longer suppress ImportError while scanning by default. If you want to suppress ImportError while scanning, you’ll now need use an onerror callback as described in the documentation.

1.0a6 (2012-04-23)

  • Don’t ignore decorated objects within their original locations if they happen to be imported into another module (remove seen set from invoke in venusian scanning). See .

1.0a5 (2012-04-21)

  • Slightly less sucky way to ignore objects during scanning that are only imported into a module but not actually defined there. See 1.0a4 change notes for rationale. Now instead of checking whether the module of the scanned object matches the module being scanned, we check whether the module of the Venusian attachment matches the module being scanned. This allows some genuine uses of imported objects as Venusian scan targets while preventing inappropriate double-scanning of objects that have a venusian attachment which just happen to be imported into other scanned modules.
  • Add dev and docs commands (ala Pyramid).

1.0a4 (2012-04-16)

  • Attempt to ignore objects during scanning that are only imported into a module but not actually defined there. This is a semantics change, but it’s the right thing to do, because I found myself facing a situation like this:

    # in a module named "one"
    from two import anotheradecoratedthing
    def adecoratedthing(): pass
    # and scanning both modules

    In this case you’d wind up with two repeated registrations for “anotherdecoratedthing”, which isn’t what anyone expects.

1.0a3 (2012-02-08)

  • Add an ignore argument to the scan method of a Scanner. This argument allows a user to ignore packages, modules, and global objects by name during a scan. See the “ignore Scan Argument” in the narrative documentation for more details.

1.0a2 (2011-09-02)

  • Close ImpLoader file handle to avoid resource warnings on Python 3.

1.0a1 (2011-08-27)

  • Python 3 compatibility.
  • Allow an onerror callback to be passed to Scanner.scan().

0.9 (2011-06-18)

0.8 (2011-04-30)

  • Normal “ test” can’t support running the venusian tests under py 2.4 or 2.5; when it scans the ‘classdecorators’ fixture, it barfs. To get around this, we used to depend on nose in setup_requires and tell “ test” to use nose by setting test_suite to “nose.collector” but we can’t anymore because folks use Venusian in systems which install from pip bundles; pip bundles do not support setup_requires. So, sorry, we’re painted into a corner; at this point you just have to know to install nose and run “ nosetests” rather than “ test”. Or just run “tox” which tests it under all Pythons.

0.7 (2011-03-16)

  • Use Pylons theme in documentation.
  • Fix orphaned pyc test on pypy.
  • Fix GitHub Issue #1: subclasses of decorated classes that do not have any decorations should not inherit the decorations of their parent classes.
  • Fix GitHub Issue #2: scans should only “find” each object once per scan, regardless of how many modules that object is imported into.

0.6 (2011-01-09)

  • Some metaclasses (Elixir’s) don’t raise an AttributeError when asked for a nonexistent attribute during a scan. We now catch all exceptions when interrogating an object for __venusian_callbacks__ rather than just AttributeError.

0.5 (2010-12-19)

  • Make codeinfo attribute available as an attribute of the AttachInfo object. It will be a tuple in the form (filename, lineno, function, sourceline) representing the context of the venusian decorator. Eg. ('/home/chrism/projects/venusian/tests/', 81, 'testCallInfo', 'add_handler(foo, bar)')

0.4 (2010-09-03)

  • Bug fix: when a venusian decorator used as a class decorator was used against both a class and a subclass of that class, the superclass and subclass would effectively share the same set of callbacks. This was not the intent: each class declaration should have its own local set of callbacks; callbacks added via decorations should not be inherited, and a superclass should not receive its subclass’ decorations.
  • Arrange test fixtures into a single directory.

0.3 (2010-06-24)

  • Ignore orphaned modules (.pyc or .pyo files without a corresponding .py file) during a scan.

0.2 (2010-04-18)

  • Add the concept of scan categories (see the “Scan Categories” section of the documentation) to allow an application to make use of more than one Venusian-using framework simultaneously.

0.1 (2010-02-15)

  • Initial release.

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