collective.monkeypatcher 1.0b2

Support for applying monkey patches late in the startup cycle by using ZCML configuration actions

Introduction

Sometimes, a monkey patch is a necessary evil.

This package makes it easier to apply a monkey patch during Zope startup. It uses the ZCML configuration machinery to ensure that patches are loaded “late” in the startup cycle, so that the original code has had time to be fully initialised and configured. This is similar to using the initialize() method in a product’s __init__.py, except it does not require that the package be a full-blown Zope 2 product with a persistent Control_Panel entry.

Applying a monkey patch

Here’s an example:

<configure
    xmlns="http://namespaces.zope.org/zope"
    xmlns:monkey="http://namespaces.plone.org/monkey"
    i18n_domain="collective.monkeypatcher">

    <include package="collective.monkeypatcher" />

    <monkey:patch
        description="This works around issue http://some.tracker.tld/ticket/123"
        class="Products.CMFPlone.CatalogTool.CatalogTool"
        original="searchResults"
        replacement=".catalog.patchedSearchResults"
        />

</configure>

In this example, we patch Plone’s CatalogTool’s searchResults() function, replacing it with our own version in catalog.py. To patch a module level function, you can use module instead of class. The original class and function/method name and the replacement symbol will be checked to ensure that they actually exist.

If patching happens too soon (or too late), use the order attribute to specify a higher (later) or lower (earlier) number. The default is 1000.

By default, DocFinderTab and other TTW API browsers will emphasize the monkey patched methods/functions, appending the docstring with “Monkey patched with ‘my.monkeypatched.function’”. If you don’t want this, you could set the docstringWarning attribute to false.

If you want to do more than just replace one function with another, you can provide your own patcher function via the handler attribute. This should be a callable like:

def apply_patch(scope, original, replacement):
    ...

Here, scope is the class/module that was specified. original is the string name of the function to replace, and replacement is the replacement function.

Handling monkey patches events

Applying a monkey patch fires an event. See the interfaces.py module. If you to handle such event add this ZCML:

<subscriber
  for="collective.monkeypatcher.interfaces.IMonkeyPatchEvent"
  handler="my.component.events.myHandler"
  />

And add a handler such as Python:

def myHandler(event):
    """see collective.monkeypatcher.interfaces.IMonkeyPatchEvent"""