78 lines
2.2 KiB
Python
78 lines
2.2 KiB
Python
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class StateTree:
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"""A dictionary-like object that tracks when values have been changed."""
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def __init__(self, dictionary: dict = None, parent: "StateTree" = None) -> None:
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"""Create a new state tree.
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If a dictionary is supplied, its values will be initialized with it and
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the tree will be marked as clean.
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If a parent is supplied, the parent will be marked as dirty when this
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tree is modified.
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"""
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self._dictionary = dictionary if dictionary else dict()
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self._parent = parent
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self._changed = False
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def dirty(self):
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"""Mark the tree as dirty.
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This is done automatically whenever an item is updated.
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"""
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self._changed = True
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if self._parent:
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self._parent.dirty()
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def clean(self):
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"""Mark the tree as clean.
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Use this method to reset the changed status of the tree once after
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you've reacted to it being updated.
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"""
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self._changed = False
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@property
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def changed(self):
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"""Returns whether the tree has been modified since the last time it was
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marked as clean."""
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return self._changed
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@property
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def dictionary(self):
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"""Returns the underlying dictionary."""
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return self._dictionary
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def __getitem__(self, *args, **kwargs):
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"""Get the value stored in a key in the tree.
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If the value is a dictionary, returns a StateTree object instead that
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will notify the parent if a change is made.
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"""
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o = self._dictionary.__getitem__(*args, **kwargs)
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if isinstance(o, dict):
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return StateTree(o, parent=self)
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else:
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return o
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def __setitem__(self, key, value):
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"""Update the value of a key in the tree.
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Marks the tree as changed if the key is new or the new value differs
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from the current value.
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"""
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if key not in self._dictionary or value != self._dictionary[key]:
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self.dirty()
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self._dictionary[key] = value
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def __repr__(self):
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return "<StateTree{}{} {}>".format(
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"^" if self._parent else "",
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"*" if self._changed else "",
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repr(self._dictionary),
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)
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