'NoneType" Error when adding layer to WebMap using Python API

[Arne_Gelfert]

Trying to add a layer (Portal item) to a webmap. The ESRI example for this I'm looking at is very simple:

streets_item = gis.content.search("LA Streets","Map Service")[0]

wm = WebMap()  # create an empty web map with a default basemap
wm.add_layer(streets_item)‍‍‍‍

Okay, so I have a web map that's not empty that I created like this:

print(type(target_item))

from arcgis.mapping import WebMap
web_map_obj = WebMap(target_item)

print(type(web_map_obj))‍‍‍‍‍‍

#>>> <class 'arcgis.gis.Item'>
#>>> <class 'arcgis.mapping._types.WebMap'>
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

The print() statements are only there to assure myself that I'm actually looking at items on and not itemId's or who knows what. So I have a legit Python web map based on on a web map item in Portal. As a check, I do...

web_map_obj.layers

# prints out all the layers (map image layers) that nelong to the Portal web map‍‍‍

 So now, I want to add another layer

newLayer = gis.content.search(query = "new layer"))[0]
# again just checking this is what I expect
print(type(newLayer))

web_map_obj.add_layer(newLayer)‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Well, this bombs... 

<class 'arcgis.gis.Item'>

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-191-62f982ec1c55> in <module>
     13     # again just checking this is what I expect
     14     print(type(newLayer))
---> 15     web_map_obj.add_layer(newLayer)

C:\Program Files\ArcGIS\Pro\bin\Python\envs\arcgispro-py3\lib\site-packages\arcgis\mapping\_types.py in add_layer(self, layer, options)
    323 
    324                 for lyr in layer.layers:  # recurse - works for all.
--> 325                     self.add_layer(lyr, options)
    326                 return True  # end add_layer execution after iterating through each layer.
    327             else:

C:\Program Files\ArcGIS\Pro\bin\Python\envs\arcgispro-py3\lib\site-packages\arcgis\mapping\_types.py in add_layer(self, layer, options)
    510                         fields_list = layer.properties.layerDefinition.fields
    511 
--> 512             for f in fields_list:
    513                 if isinstance(f, dict) or isinstance(f, PropertyMap):
    514                     field_dict = {'fieldName': f['name'],

TypeError: 'NoneType' object is not iterable
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

What's wrong with what I'm doing? I realize there is also arcgis.gis.Layer. Do I first need to create a Layer from the item and then add that to the web map maybe?

[Arne_Gelfert]

So it looks like the following works:

newLayer_item = gis.content.search(query = "new layer"))[0]

###############################################
# the following line is new and made this work
newLayer = arcgis.gis.Layer(newLayer_item)
###############################################
web_map_obj.add_layer(newLayer)

# Now I can see the new layers with
web_map_obj.layers‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Anyone know if the above referenced original ESRI example will ever work and if I was doing something wrong?

[JoshuaBixby]

Where are you executing your code from, Python interactive windows in ArcGIS Pro, Python command prompt, Jupyter notebook?

[Arne_Gelfert]

Jupyter Notebooks.

[JoshuaBixby]

Regarding newLayer_item, what exactly is it?  I get the Esri examples to work in Jupyter, after a minor change to search outside my org, so I am wondering about your layer.

[Arne_Gelfert]

NewLayer is a Portal item that references a Map Service on our federated GIS Server. Where this all started was when I looked into copying a web map item from one Portal environment (Test) to another (Prod) and then trying to replace some map services .

[JoshuaBixby]

Since the Esri examples work for me in Jupyter, and I can't test directly using your data, I don't have any other suggestions/ideas at this point.  Maybe a Pro version thing.  What version of Pro are you running?

[Arne_Gelfert]

This is Pro 2.5... I might try upgrading or at checking which version of arcgis modules my conda environment is using.

[Arne_Gelfert]

Turns out the syntax of the ESRI example works when adding an item (as layer) to web map using add_layer() works when it was created as empty new web map like this:

webmap = ‍Webmap()‍

But not when the web map was created off another item and already has some layers...

webmap = Webmap(item)‍

This may be explained somewhere in ESRI documentation. Good to know!