def get_gene_by_mrna(self, ctx, ref, mrna_id_list):
"""
Retrieves gene Feature IDs for given mRNA Feature IDs.
@param mrna_id_list List of mRNA Feature IDS for which to retrieve gene IDs.
If empty, returns all mRNA/gene mappings.
@return Mapping of mRNA Feature IDs to gene Feature IDs.
:param ref: instance of type "ObjectReference"
:param mrna_id_list: instance of list of String
:returns: instance of mapping from String to String
"""
# ctx is the context object
# return variables are: returnVal
#BEGIN get_gene_by_mrna
ga = GenomeAnnotationAPI_local(self.services, ctx['token'], ref)
if not mrna_id_list:
returnVal = ga.get_gene_by_mrna([])
else:
returnVal = ga.get_gene_by_mrna(mrna_id_list)
#END get_gene_by_mrna
# At some point might do deeper type checking...
if not isinstance(returnVal, dict):
raise ValueError('Method get_gene_by_mrna return value ' +
'returnVal is not type dict as required.')
# return the results
return [returnVal]
