'Returns a list of your Lambda functions. For each function,
the response includes the function configuration information.
You must use GetFunction to retrieve the code for your
function.
This operation requires permission for the
`lambda:ListFunctions` action.
:type marker: string
:param marker: Optional string. An opaque pagination token returned
from a previous `ListFunctions` operation. If present, indicates
where to continue the listing.
:type max_items: integer
:param max_items: Optional integer. Specifies the maximum number of AWS
Lambda functions to return in response. This parameter value must
be greater than 0.'

def list_functions(self, marker=None, max_items=None):

    uri = '/2014-11-13/functions/'
    params = {}
    headers = {}
    query_params = {}
    if (marker is not None):
        query_params['Marker'] = marker
    if (max_items is not None):
        query_params['MaxItems'] = max_items
    return self.make_request('GET', uri, expected_status=200, data=json.dumps(params), headers=headers, params=query_params)
