compiler.py 文件源码

def compiles(class_, *specs):
    """Register a function as a compiler for a
    given :class:`.ClauseElement` type."""

    def decorate(fn):
        # get an existing @compiles handler
        existing = class_.__dict__.get('_compiler_dispatcher', None)

        # get the original handler.  All ClauseElement classes have one
        # of these, but some TypeEngine classes will not.
        existing_dispatch = getattr(class_, '_compiler_dispatch', None)

        if not existing:
            existing = _dispatcher()

            if existing_dispatch:
                def _wrap_existing_dispatch(element, compiler, **kw):
                    try:
                        return existing_dispatch(element, compiler, **kw)
                    except exc.UnsupportedCompilationError:
                        raise exc.CompileError(
                            "%s construct has no default "
                            "compilation handler." % type(element))
                existing.specs['default'] = _wrap_existing_dispatch

            # TODO: why is the lambda needed ?
            setattr(class_, '_compiler_dispatch',
                    lambda *arg, **kw: existing(*arg, **kw))
            setattr(class_, '_compiler_dispatcher', existing)

        if specs:
            for s in specs:
                existing.specs[s] = fn

        else:
            existing.specs['default'] = fn
        return fn
    return decorate