'Compiles self.PATTERN into self.pattern.
Subclass may override if it doesn\'t want to use
self.{pattern,PATTERN} in .match().'

def compile_pattern(self):

    if (self.PATTERN is not None):
        PC = PatternCompiler()
        (self.pattern, self.pattern_tree) = PC.compile_pattern(self.PATTERN, with_tree=True)
