Supporting Search Query Syntax

It's very easy to add support for search-engine like syntax in your program.
The idea is to convert the query to a Python expression and then evaluate it.

We'll support the following syntax:

word1 word2       - word1 and word2
word1 AND word2   - word1 and word2
word1 word2       - word1 and word2
word1 OR word2    - word1 ord word2
NOT word          - Not containing word

The code is very simple:

def is_operator(token):
  return token in set(["and", "not", "or", "(", ")"])

def should_insert_and(expr, token):
  if not expr:
      return 0

  if is_operator(expr[-1]):
      return 0

  if is_operator(token):
      return 0

  return 1

def match(query, text):
  words = set(text.lower().split())

  expr = []
  for token in query.lower().split():

      if should_insert_and(expr, token):
          expr.append("and")

      if is_operator(token):
          expr.append(token)
      else:
          expr.append(token in words)

  py_expr = " ".join(map(str, expr))
  return eval(py_expr)

def test():
  assert match("a", "a"), "a --- a"
  assert not match("a", ""), " --- a"
  assert match("a AND b", "a c b"), "a c b --- a AND b"
  assert not match("a AND b", "a c"), "a c --- a AND b"
  assert match("NOT ( a OR b )", "z"), "z --- NOT ( a OR b )"
  assert match("a OR b", "b"), "b --- a OR b"

Notes:
1. We don't do any fancy tokenization (text and query), but in most cases this should be enough.
2. We place an AND where it's missing.