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# Copyright (c) 2010 testtools developers. See LICENSE for details.
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"""Helpers for monkey-patching Python code."""
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class MonkeyPatcher(object):
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"""A set of monkey-patches that can be applied and removed all together.
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Use this to cover up attributes with new objects. Particularly useful for
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testing difficult code.
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# Marker used to indicate that the patched attribute did not exist on the
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# object before we patched it.
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_NO_SUCH_ATTRIBUTE = object()
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def __init__(self, *patches):
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"""Construct a `MonkeyPatcher`.
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:param patches: The patches to apply, each should be (obj, name,
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new_value). Providing patches here is equivalent to calling
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# List of patches to apply in (obj, name, value).
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self._patches_to_apply = []
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# List of the original values for things that have been patched.
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# (obj, name, value) format.
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self.add_patch(*patch)
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def add_patch(self, obj, name, value):
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"""Add a patch to overwrite 'name' on 'obj' with 'value'.
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The attribute C{name} on C{obj} will be assigned to C{value} when
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C{patch} is called or during C{run_with_patches}.
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You can restore the original values with a call to restore().
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self._patches_to_apply.append((obj, name, value))
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"""Apply all of the patches that have been specified with `add_patch`.
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Reverse this operation using L{restore}.
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for obj, name, value in self._patches_to_apply:
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original_value = getattr(obj, name, self._NO_SUCH_ATTRIBUTE)
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self._originals.append((obj, name, original_value))
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setattr(obj, name, value)
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"""Restore all original values to any patched objects.
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If the patched attribute did not exist on an object before it was
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patched, `restore` will delete the attribute so as to return the
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object to its original state.
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while self._originals:
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obj, name, value = self._originals.pop()
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if value is self._NO_SUCH_ATTRIBUTE:
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setattr(obj, name, value)
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def run_with_patches(self, f, *args, **kw):
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"""Run 'f' with the given args and kwargs with all patches applied.
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Restores all objects to their original state when finished.
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def patch(obj, attribute, value):
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"""Set 'obj.attribute' to 'value' and return a callable to restore 'obj'.
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If 'attribute' is not set on 'obj' already, then the returned callable
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will delete the attribute when called.
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:param obj: An object to monkey-patch.
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:param attribute: The name of the attribute to patch.
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:param value: The value to set 'obj.attribute' to.
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:return: A nullary callable that, when run, will restore 'obj' to its
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patcher = MonkeyPatcher((obj, attribute, value))
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return patcher.restore
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python-for-subunit2junitxml/testtools/monkey.py
