cti-python-stix2/stix2/equivalence/pattern/transform/__init__.py

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"""
Generic AST transformation classes.
.. autosummary::
:toctree: transform
comparison
observation
specials
|
"""
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class Transformer:
"""
Base class for AST transformers.
"""
def transform(self, ast):
"""
Transform the given AST and return the resulting AST.
:param ast: The AST to transform
:return: A 2-tuple: the transformed AST and a boolean indicating whether
the transformation actually changed anything. The change detection
is useful in situations where a transformation needs to be repeated
until the AST stops changing.
"""
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raise NotImplementedError("transform")
class ChainTransformer(Transformer):
"""
A composite transformer which consists of a sequence of sub-transformers.
Applying this transformer applies all sub-transformers in sequence, as
a group.
"""
def __init__(self, *transformers):
self.__transformers = transformers
def transform(self, ast):
changed = False
for transformer in self.__transformers:
ast, this_changed = transformer.transform(ast)
if this_changed:
changed = True
return ast, changed
class SettleTransformer(Transformer):
"""
A transformer that repeatedly performs a transformation until that
transformation no longer changes the AST. I.e. the AST has "settled".
"""
def __init__(self, transform):
self.__transformer = transform
def transform(self, ast):
changed = False
ast, this_changed = self.__transformer.transform(ast)
while this_changed:
changed = True
ast, this_changed = self.__transformer.transform(ast)
return ast, changed