Collecting all the (relevant) things!

Find all elements of a type in active view

OfClass docs:

http://www.revitapidocs.com/2018.1/b0a5f22c-6951-c3af-cd29-1f28f574035d.htm

Autodesk.Revit.DB Namespace, for categories to be filtered:

http://www.revitapidocs.com/2018.1/87546ba7-461b-c646-cbb1-2cb8f5bff8b2.htm

##Where doc = __revit__.ActiveUIDocument.Document
elementList = DB.FilteredElementCollector(doc, selected_view.Id)\
.OfClass(DB.IndependentTag)\
.ToElements()

Another collecting walls:

collector = FilteredElementCollector(doc)\
.OfCategory(BuiltInCategory.OST_Walls)\
.WhereElementIsNotElementType()\
.ToElements()