where.py 文件源码

def _prepare_data(self, data):
        """
        Prepare data for addition to the tree. If the data is a list or tuple,
        it is expected to be of the form (obj, lookup_type, value), where obj
        is a Constraint object, and is then slightly munged before being
        stored (to avoid storing any reference to field objects). Otherwise,
        the 'data' is stored unchanged and can be any class with an 'as_sql()'
        method.
        """
        if not isinstance(data, (list, tuple)):
            return data
        obj, lookup_type, value = data
        if isinstance(value, collections.Iterator):
            # Consume any generators immediately, so that we can determine
            # emptiness and transform any non-empty values correctly.
            value = list(value)

        # The "value_annotation" parameter is used to pass auxiliary information
        # about the value(s) to the query construction. Specifically, datetime
        # and empty values need special handling. Other types could be used
        # here in the future (using Python types is suggested for consistency).
        if (isinstance(value, datetime.datetime)
                or (isinstance(obj.field, DateTimeField) and lookup_type != 'isnull')):
            value_annotation = datetime.datetime
        elif hasattr(value, 'value_annotation'):
            value_annotation = value.value_annotation
        else:
            value_annotation = bool(value)

        if hasattr(obj, 'prepare'):
            value = obj.prepare(lookup_type, value)
        return (obj, lookup_type, value_annotation, value)