Of course, the inquisitive would soon discover that the difference between a polygon and a polyline is a simple word in the help files...
features.append( arcpy.(Polyline or Polygon)( arcpy.Array([arcpy.Point(*coords) for coords in feature])))
Polygon—Help | ArcGIS for Desktop
Polyline—Help | ArcGIS for Desktop
but that would be overkill for general use