table.py 文件源码

def Q(**mapping):
    """A Q object represents an AND'd together query using boto3's Attr object, based on a set of keyword arguments that
    support the full access to the operations (eq, ne, between, etc) as well as nested attributes.

    It can be used input to both scan operations as well as update conditions.
    """
    expression = None

    while len(mapping):
        attr, value = mapping.popitem()

        parts = attr.split('__')
        attr = Attr(parts.pop(0))
        op = 'eq'

        while len(parts):
            if not hasattr(attr, parts[0]):
                # this is a nested field, extend the attr
                attr = Attr('.'.join([attr.name, parts.pop(0)]))
            else:
                op = parts.pop(0)
                break

        assert len(parts) == 0, "Left over parts after parsing query attr"

        op = getattr(attr, op)
        try:
            attr_expression = op(value)
        except TypeError:
            # A TypeError calling our attr op likely means we're invoking exists, not_exists or another op that
            # doesn't take an arg or takes multiple args. If our value is True then we try to re-call the op
            # function without any arguments, if our value is a list we use it as the arguments for the function,
            # otherwise we bubble it up.
            if value is True:
                attr_expression = op()
            elif isinstance(value, collections.Iterable):
                attr_expression = op(*value)
            else:
                raise

        try:
            expression = expression & attr_expression
        except TypeError:
            expression = attr_expression

    return expression