Hello Dynamo Friends 
In some python scripts i have the problem that there are many nulls in my output list:
So i would like to avoid getting these nulls or remove those nulls.
I tried “is not None” and “!= None” without success:
outlist = []
views = FilteredElementCollector(doc).OfClass(View).ToElements()
for view in views:
if view != None:
outlist.append(view)
OUT = outlist
Happy about any advice
i have no solution just a direction. My idea is filter by object Type and kick out else… …but it does not work 
import sys
import clr
clr.AddReference('RevitAPI')
from Autodesk.Revit.DB import *
from Autodesk.Revit.DB.Structure import *
clr.AddReference('RevitAPIUI')
from Autodesk.Revit.UI import *
clr.AddReference('System')
from System.Collections.Generic import List
clr.AddReference('RevitNodes')
import Revit
clr.ImportExtensions(Revit.GeometryConversion)
clr.ImportExtensions(Revit.Elements)
clr.AddReference('RevitServices')
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager
doc = DocumentManager.Instance.CurrentDBDocument
uidoc=DocumentManager.Instance.CurrentUIApplication.ActiveUIDocument
outlist = []
views = FilteredElementCollector(doc).OfClass(View).ToElements()
otyp = []
for i in views:
otyp.append(i.GetType())
for view in otyp:
if view == Revit.Elements.Views.AreaPlanView:
outlist.append(True)
elif view == Revit.Elements.Views.Legend:
outlist.append(True)
elif view != Revit.Elements.Views.ScheduleView:
outlist.append(False)
elif view == Revit.Elements.Views.View:
outlist.append(True)
elif view != Revit.Elements.Views.AxonometricView:
outlist.append(False)
elif view != Revit.Elements.Views.CeilingPlanView:
outlist.append(False)
elif view != Revit.Elements.Views.StructuralPlanView:
outlist.append(False)
elif view != Revit.Elements.Views.PerspectiveView:
outlist.append(False)
elif view != Revit.Elements.Views.DraftingView:
outlist.append(False)
elif view != Revit.Elements.Views.FloorPlanView:
outlist.append(False)
elif view != Revit.Elements.Views.Sheet:
outlist.append(False)
elif view != Revit.Elements.Views.SectionView:
outlist.append(False)
elif view != Revit.Elements.Views.View3D:
outlist.append(False)
else:
outlist.append(True)
OUT = outlist,otyp
Oh now it came to mind, that @Alban_de_Chasteigner has a List.Clean node that also contains more information on this topic:
Clean list or list of lists of all None or Empty lists in Python - Stack Overflow
def ClearList(primList):
result = []
for sublist in primList:
if sublist is "":
continue
elif sublist is None:
continue
if isinstance(sublist, list):
sublist = ClearList(sublist)
if not sublist:
continue
result.append(sublist)
return result
OUT = ClearList(IN[0])
Hi,
You could also use the filter(None, list) function.
outlist = []
views = FilteredElementCollector(doc).OfClass(View).ToElements()
OUT = filter(None,views)
the NULLs still remain
the OUT Dynamo Wrapper is capricious with certain objects
here a solution
import sys
import clr
import System
clr.AddReference('RevitAPI')
from Autodesk.Revit.DB import *
clr.AddReference('RevitServices')
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager
doc = DocumentManager.Instance.CurrentDBDocument
uidoc=DocumentManager.Instance.CurrentUIApplication.ActiveUIDocument
ueWrapper = next((m for m in clr.GetClrType(Revit.Elements.ElementWrapper)\
.GetMethods() if m.Name == "Wrap"), None)
if ueWrapper is None:
raise Exception("Error Method", "method 'Revit.Elements.ElementWrapper.Wrap' not found")
views = FilteredElementCollector(doc).OfClass(View).ToElements()
outlist = []
for i in views:
iswrapable = Revit.Elements.ElementWrapper.Wrap(i, True)
if iswrapable is None :
outlist.append(ueWrapper.Invoke(None, (i, True) ))
else:
outlist.append(i)
OUT = outlist
But i have no idea whats going on 
Whats a wrapper?
So i found out that it´s the converting of 3D views to elements with the FilteredElementCollector is the problem:
And i solved that by dropping 3D viewtypes:
outlist=[]
views = FilteredElementCollector(doc).OfClass(View).ToElements()
for view in views:
x=view.ViewType
if view.ViewType != ViewType.ThreeD:
outlist.append(view)
OUT = outlist
Probably 3D view templates.
An old « bug » of Dynamo for Revit.
Hi @gerhard.p maybe try also skip the project browser and system browser that are in your list. Cheers
I provide my python function version to collect all views in a document and also removing the funny nulls but showing the all the corresponding view types in the document, that means 3D View templates , system browser, project browser are available with ID 
.
I tried in a project and I got this list of view types:
[0] CeilingPlan
[1] Detail
[2] DrawingSheet
[3] Elevation
[4] FloorPlan
[5] Legend
[6] ProjectBrowser
[7] Schedule
[8] Section
[9] SystemBrowser
[10] ThreeD
[11] 3DViewTemplate
this how it displays in dynamo node the results:
thanks to the suggestion of @c.poupin I could do some investigation and make it work as wanted:
import sys
import clr
import System
clr.AddReference('RevitAPI')
from Autodesk.Revit.DB import *
import Autodesk
clr.AddReference("RevitNodes")
import Revit
clr.AddReference('RevitServices')
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager
doc = DocumentManager.Instance.CurrentDBDocument
uidoc=DocumentManager.Instance.CurrentUIApplication.ActiveUIDocument
def WrapUnwrapElements(elements):
# Get method Revit.Elements.ElementWrapper.Wrap
ueWrapper = next((m for m in clr.GetClrType(Revit.Elements.ElementWrapper)\
.GetMethods() if m.Name == "Wrap"), None)
if ueWrapper is None:
raise Exception("Error Method", "method 'Revit.Elements.ElementWrapper.Wrap' not found")
outlist = []
for i in elements:
iswrapable = Revit.Elements.ElementWrapper.Wrap(i, True)
if iswrapable is None :
outlist.append(ueWrapper.Invoke(None, (i, True)))
else:
outlist.append(i)
return outlist
def GetViewType(view):
if hasattr(view, "ViewType"): return str(view.ViewType)
else: return None
def GetAllViews(doc):
collector = FilteredElementCollector(doc).OfClass(View).ToElements()
# Apply the WrapUnwrapElements function
wrapped_views = WrapUnwrapElements(collector)
allviews = [view for view in wrapped_views if isinstance(view, Autodesk.Revit.DB.View) or 'View3D' == str(view)]
view_dict = {}
for view in allviews:
view_type = GetViewType(view)
if view_type is None: # Handle views with None type
view_type = "3DViewTemplate"
if view_type not in view_dict:
view_dict[view_type] = [] # initialize the list for this view type
view_dict[view_type].append(view) # append the view to its respective list
return view_dict
def GetAllViewTemplates(doc):
collector = FilteredElementCollector(doc).OfClass(View).ToElements()
# Apply the WrapUnwrapElements function
wrapped_views = WrapUnwrapElements(collector)
templates = [view for view in wrapped_views if (isinstance(view, Autodesk.Revit.DB.View) and hasattr(view, "IsTemplate") and view.IsTemplate) or 'View3D' == str(view)]
view_dict = {}
for view in templates:
view_type = GetViewType(view)
if view_type is None: # Handle views with None type
view_type = "3DViewTemplate"
if view_type not in view_dict:
view_dict[view_type] = [] # initialize the list for this view type
view_dict[view_type].append(view) # append the view to its respective list
return view_dict
OUT = {"All Views in Document": GetAllViews(doc), "All View Templates in Document": GetAllViewTemplates(doc)}