133 lines
4.8 KiB
Python
133 lines
4.8 KiB
Python
"""
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A class for storing a tree graph. Primarily used for filter constructs in the
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ORM.
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"""
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import copy
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class Node(object):
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"""
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A single internal node in the tree graph. A Node should be viewed as a
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connection (the root) with the children being either leaf nodes or other
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Node instances.
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"""
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# Standard connector type. Clients usually won't use this at all and
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# subclasses will usually override the value.
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default = 'DEFAULT'
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def __init__(self, children=None, connector=None, negated=False):
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"""
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Constructs a new Node. If no connector is given, the default will be
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used.
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"""
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self.children = children[:] if children else []
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self.connector = connector or self.default
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self.negated = negated
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# We need this because of django.db.models.query_utils.Q. Q. __init__() is
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# problematic, but it is a natural Node subclass in all other respects.
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@classmethod
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def _new_instance(cls, children=None, connector=None, negated=False):
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"""
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This is called to create a new instance of this class when we need new
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Nodes (or subclasses) in the internal code in this class. Normally, it
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just shadows __init__(). However, subclasses with an __init__ signature
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that is not an extension of Node.__init__ might need to implement this
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method to allow a Node to create a new instance of them (if they have
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any extra setting up to do).
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"""
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obj = Node(children, connector, negated)
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obj.__class__ = cls
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return obj
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def __str__(self):
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if self.negated:
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return '(NOT (%s: %s))' % (self.connector, ', '.join(str(c) for c
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in self.children))
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return '(%s: %s)' % (self.connector, ', '.join(str(c) for c in
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self.children))
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def __repr__(self):
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return "<%s: %s>" % (self.__class__.__name__, self)
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def __deepcopy__(self, memodict):
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"""
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Utility method used by copy.deepcopy().
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"""
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obj = Node(connector=self.connector, negated=self.negated)
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obj.__class__ = self.__class__
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obj.children = copy.deepcopy(self.children, memodict)
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return obj
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def __len__(self):
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"""
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The size of a node if the number of children it has.
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"""
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return len(self.children)
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def __bool__(self):
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"""
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For truth value testing.
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"""
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return bool(self.children)
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def __nonzero__(self): # Python 2 compatibility
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return type(self).__bool__(self)
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def __contains__(self, other):
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"""
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Returns True is 'other' is a direct child of this instance.
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"""
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return other in self.children
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def add(self, data, conn_type, squash=True):
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"""
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Combines this tree and the data represented by data using the
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connector conn_type. The combine is done by squashing the node other
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away if possible.
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This tree (self) will never be pushed to a child node of the
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combined tree, nor will the connector or negated properties change.
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The function returns a node which can be used in place of data
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regardless if the node other got squashed or not.
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If `squash` is False the data is prepared and added as a child to
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this tree without further logic.
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"""
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if data in self.children:
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return data
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if not squash:
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self.children.append(data)
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return data
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if self.connector == conn_type:
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# We can reuse self.children to append or squash the node other.
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if (isinstance(data, Node) and not data.negated
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and (data.connector == conn_type or len(data) == 1)):
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# We can squash the other node's children directly into this
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# node. We are just doing (AB)(CD) == (ABCD) here, with the
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# addition that if the length of the other node is 1 the
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# connector doesn't matter. However, for the len(self) == 1
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# case we don't want to do the squashing, as it would alter
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# self.connector.
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self.children.extend(data.children)
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return self
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else:
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# We could use perhaps additional logic here to see if some
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# children could be used for pushdown here.
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self.children.append(data)
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return data
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else:
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obj = self._new_instance(self.children, self.connector,
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self.negated)
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self.connector = conn_type
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self.children = [obj, data]
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return data
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def negate(self):
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"""
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Negate the sense of the root connector.
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"""
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self.negated = not self.negated
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