'Initializer.
Takes an optional alternative filename for the pattern grammar.'

def __init__(self, grammar_file=_PATTERN_GRAMMAR_FILE):

    self.grammar = driver.load_grammar(grammar_file)
    self.syms = pygram.Symbols(self.grammar)
    self.pygrammar = pygram.python_grammar
    self.pysyms = pygram.python_symbols
    self.driver = driver.Driver(self.grammar, convert=pattern_convert)
