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btm_matcher.py
"""A bottom-up tree matching algorithm implementation meant to speed up 2to3's matching process. After the tree patterns are reduced to their rarest linear path, a linear Aho-Corasick automaton is created. The linear automaton traverses the linear paths from the leaves to the root of the AST and returns a set of nodes for further matching. This reduces significantly the number of candidate nodes.""" __author__ = "George Boutsioukis <gboutsioukis@gmail.com>" import logging import itertools from collections import defaultdict from . import pytree from .btm_utils import reduce_tree class BMNode(object): """Class for a node of the Aho-Corasick automaton used in matching""" count = itertools.count() def __init__(self): self.transition_table = {} self.fixers = [] self.id = next(BMNode.count) self.content = '' class BottomMatcher(object): """The main matcher class. After instantiating the patterns should be added using the add_fixer method""" def __init__(self): self.match = set() self.root = BMNode() self.nodes = [self.root] self.fixers = [] self.logger = logging.getLogger("RefactoringTool") def add_fixer(self, fixer): """Reduces a fixer's pattern tree to a linear path and adds it to the matcher(a common Aho-Corasick automaton). The fixer is appended on the matching states and called when they are reached""" self.fixers.append(fixer) tree = reduce_tree(fixer.pattern_tree) linear = tree.get_linear_subpattern() match_nodes = self.add(linear, start=self.root) for match_node in match_nodes: match_node.fixers.append(fixer) def add(self, pattern, start): "Recursively adds a linear pattern to the AC automaton" #print("adding pattern", pattern, "to", start) if not pattern: #print("empty pattern") return [start] if isinstance(pattern[0], tuple): #alternatives #print("alternatives") match_nodes = [] for alternative in pattern[0]: #add all alternatives, and add the rest of the pattern #to each end node end_nodes = self.add(alternative, start=start) for end in end_nodes: match_nodes.extend(self.add(pattern[1:], end)) return match_nodes else: #single token #not last if pattern[0] not in start.transition_table: #transition did not exist, create new next_node = BMNode() start.transition_table[pattern[0]] = next_node else: #transition exists already, follow next_node = start.transition_table[pattern[0]] if pattern[1:]: end_nodes = self.add(pattern[1:], start=next_node) else: end_nodes = [next_node] return end_nodes def run(self, leaves): """The main interface with the bottom matcher. The tree is traversed from the bottom using the constructed automaton. Nodes are only checked once as the tree is retraversed. When the automaton fails, we give it one more shot(in case the above tree matches as a whole with the rejected leaf), then we break for the next leaf. There is the special case of multiple arguments(see code comments) where we recheck the nodes Args: The leaves of the AST tree to be matched Returns: A dictionary of node matches with fixers as the keys """ current_ac_node = self.root results = defaultdict(list) for leaf in leaves: current_ast_node = leaf while current_ast_node: current_ast_node.was_checked = True for child in current_ast_node.children: # multiple statements, recheck if isinstance(child, pytree.Leaf) and child.value == ";": current_ast_node.was_checked = False break if current_ast_node.type == 1: #name node_token = current_ast_node.value else: node_token = current_ast_node.type if node_token in current_ac_node.transition_table: #token matches current_ac_node = current_ac_node.transition_table[node_token] for fixer in current_ac_node.fixers: results[fixer].append(current_ast_node) else: #matching failed, reset automaton current_ac_node = self.root if (current_ast_node.parent is not None and current_ast_node.parent.was_checked): #the rest of the tree upwards has been checked, next leaf break #recheck the rejected node once from the root if node_token in current_ac_node.transition_table: #token matches current_ac_node = current_ac_node.transition_table[node_token] for fixer in current_ac_node.fixers: results[fixer].append(current_ast_node) current_ast_node = current_ast_node.parent return results def print_ac(self): "Prints a graphviz diagram of the BM automaton(for debugging)" print("digraph g{") def print_node(node): for subnode_key in node.transition_table.keys(): subnode = node.transition_table[subnode_key] print("%d -> %d [label=%s] //%s" % (node.id, subnode.id, type_repr(subnode_key), str(subnode.fixers))) if subnode_key == 1: print(subnode.content) print_node(subnode) print_node(self.root) print("}") # taken from pytree.py for debugging; only used by print_ac _type_reprs = {} def type_repr(type_num): global _type_reprs if not _type_reprs: from .pygram import python_symbols # printing tokens is possible but not as useful # from .pgen2 import token // token.__dict__.items(): for name, val in python_symbols.__dict__.items(): if type(val) == int: _type_reprs[val] = name return _type_reprs.setdefault(type_num, type_num)
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