<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def getSampleTypes(self, active_only=True):
 """Return all sampletypes """

        catalog = api.get_tool("bika_setup_catalog")
        query = {
            "portal_type": "SampleType",
            # N.B. The `sortable_title` index sorts case sensitive. Since there
            #      is no sort key for sample types, it makes more sense to sort
            #      them alphabetically in the selection
            "sort_on": "title",
            "sort_order": "ascending"
        }
        results = catalog(query)
        if active_only:
            results = filter(api.is_active, results)
        sampletypes = map(
            lambda brain: (brain.UID, brain.Title), results)
        return DisplayList(sampletypes)