ast_to_regexp.py

def create_rule(rule, ignore_case=False):
    """ 
    Use Python's AST parser to generate a tree which we'll traverse to create a
    regular expression.
    """
    results = parser.tokens(rule.strip())
    ast_string = ''

    unicode_strings = []
    
    for token in results:
        if token.type == 'OR':
            ast_string += '+' 
        elif token.type == 'AND':
            ast_string += '*' 
        else:
            try:
                ast_string += token.value.decode('ascii')
            except:
                ast_string += 'PLACEHOLDER%s' % len(unicode_strings)
                unicode_strings.append(token.value)
    
    tree = ast.parse(ast_string)
    root = tree.body[0]
    regexp = process(root)

    # Check if we have to replace any strings.
    for idx, u in enumerate(unicode_strings):
        regexp = regexp.replace('PLACEHOLDER%s' % idx, u)

    if ignore_case:
        return re.compile(regexp, re.IGNORECASE)
    else:
        return re.compile(regexp)