'Gets the expressions configured for the search domain. Can be
limited to specific expressions by name. By default, shows all
expressions and includes any pending changes to the
configuration. Set the `Deployed` option to `True` to show the
active configuration and exclude pending changes. For more
information, see `Configuring Expressions`_ in the Amazon
CloudSearch Developer Guide .
:type domain_name: string
:param domain_name: The name of the domain you want to describe.
:type expression_names: list
:param expression_names: Limits the `DescribeExpressions` response to
the specified expressions. If not specified, all expressions are
shown.
:type deployed: boolean
:param deployed: Whether to display the deployed configuration (
`True`) or include any pending changes ( `False`). Defaults to
`False`.'

def describe_expressions(self, domain_name, expression_names=None, deployed=None):

    params = {'DomainName': domain_name}
    if (expression_names is not None):
        self.build_list_params(params, expression_names, 'ExpressionNames.member')
    if (deployed is not None):
        params['Deployed'] = str(deployed).lower()
    return self._make_request(action='DescribeExpressions', verb='POST', path='/', params=params)
