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# Natural Language Toolkit: Text Trees
#
# Copyright (C) 2001-2023 NLTK Project
# Author: Edward Loper <[email protected]>
# Steven Bird <[email protected]>
# Peter Ljunglöf <[email protected]>
# Tom Aarsen <>
# URL: <https://www.nltk.org/>
# For license information, see LICENSE.TXT
from nltk.probability import ProbabilisticMixIn
from nltk.tree.parented import MultiParentedTree, ParentedTree
from nltk.tree.tree import Tree
class ImmutableTree(Tree):
def __init__(self, node, children=None):
super().__init__(node, children)
# Precompute our hash value. This ensures that we're really
# immutable. It also means we only have to calculate it once.
try:
self._hash = hash((self._label, tuple(self)))
except (TypeError, ValueError) as e:
raise ValueError(
"%s: node value and children " "must be immutable" % type(self).__name__
) from e
def __setitem__(self, index, value):
raise ValueError("%s may not be modified" % type(self).__name__)
def __setslice__(self, i, j, value):
raise ValueError("%s may not be modified" % type(self).__name__)
def __delitem__(self, index):
raise ValueError("%s may not be modified" % type(self).__name__)
def __delslice__(self, i, j):
raise ValueError("%s may not be modified" % type(self).__name__)
def __iadd__(self, other):
raise ValueError("%s may not be modified" % type(self).__name__)
def __imul__(self, other):
raise ValueError("%s may not be modified" % type(self).__name__)
def append(self, v):
raise ValueError("%s may not be modified" % type(self).__name__)
def extend(self, v):
raise ValueError("%s may not be modified" % type(self).__name__)
def pop(self, v=None):
raise ValueError("%s may not be modified" % type(self).__name__)
def remove(self, v):
raise ValueError("%s may not be modified" % type(self).__name__)
def reverse(self):
raise ValueError("%s may not be modified" % type(self).__name__)
def sort(self):
raise ValueError("%s may not be modified" % type(self).__name__)
def __hash__(self):
return self._hash
def set_label(self, value):
"""
Set the node label. This will only succeed the first time the
node label is set, which should occur in ImmutableTree.__init__().
"""
if hasattr(self, "_label"):
raise ValueError("%s may not be modified" % type(self).__name__)
self._label = value
class ImmutableProbabilisticTree(ImmutableTree, ProbabilisticMixIn):
def __init__(self, node, children=None, **prob_kwargs):
ImmutableTree.__init__(self, node, children)
ProbabilisticMixIn.__init__(self, **prob_kwargs)
self._hash = hash((self._label, tuple(self), self.prob()))
# We have to patch up these methods to make them work right:
def _frozen_class(self):
return ImmutableProbabilisticTree
def __repr__(self):
return f"{Tree.__repr__(self)} [{self.prob()}]"
def __str__(self):
return f"{self.pformat(margin=60)} [{self.prob()}]"
def copy(self, deep=False):
if not deep:
return type(self)(self._label, self, prob=self.prob())
else:
return type(self).convert(self)
@classmethod
def convert(cls, val):
if isinstance(val, Tree):
children = [cls.convert(child) for child in val]
if isinstance(val, ProbabilisticMixIn):
return cls(val._label, children, prob=val.prob())
else:
return cls(val._label, children, prob=1.0)
else:
return val
class ImmutableParentedTree(ImmutableTree, ParentedTree):
pass
class ImmutableMultiParentedTree(ImmutableTree, MultiParentedTree):
pass
__all__ = [
"ImmutableProbabilisticTree",
"ImmutableTree",
"ImmutableParentedTree",
"ImmutableMultiParentedTree",
]
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