elements.py 文件源码

def __init__(self, field, expr, **kwargs):
        """Return a :class:`.Extract` construct.

        This is typically available as :func:`.extract`
        as well as ``func.extract`` from the
        :data:`.func` namespace.

        """
        self.type = type_api.INTEGERTYPE
        self.field = field
        self.expr = _literal_as_binds(expr, None)