class Searcher(object):
def __init__(self, dictionary_file, postings_file):
self.dictionary = Dictionary(dictionary_file)
self.postings = Postings(postings_file)
self.dictionary.load()
self.all_docs = self.postings.load_list(0)
#evaluates a query assuming it is in RPN
def evaluate_query(self, parsed_query):
stack = []
while (len(parsed_query) != 0):
element = parsed_query.pop(0)
if element == 'NOT':
operand = stack.pop()
stack.append(self.evaluate_NOT(operand))
elif element == 'AND':
first_operand = stack.pop()
second_operand = stack.pop()
stack.append(self.evaluate_AND(first_operand, second_operand))
elif element == 'OR':
first_operand = stack.pop()
second_operand = stack.pop()
stack.append(self.evaluate_OR(first_operand, second_operand))
else:
stack.append(element)
value = stack.pop()
if not isinstance(value, list):
offset = self.dictionary.get_offset(value)
value = self.postings.load_list(offset)
return value
def evaluate_AND(self, first, second):
if not isinstance(first, list):
offset = self.dictionary.get_offset(first)
first = self.postings.load_list(offset)
if not isinstance(second, list):
offset = self.dictionary.get_offset(second)
second = self.postings.load_list(offset)
return skip_intersection(first, second)
def evaluate_OR(self, first, second):
if not isinstance(first, list):
offset = self.dictionary.get_offset(first)
first = self.postings.load_list(offset)
if not isinstance(second, list):
offset = self.dictionary.get_offset(second)
second = self.postings.load_list(offset)
return union(first, second)
def evaluate_NOT(self, operand):
if not isinstance(operand, list):
offset = self.dictionary.get_offset(operand)
operand = self.postings.load_list(offset)
return difference(self.all_docs, operand)
