How to update a definition query in a web map using python arcpy

[SanchezNuñez]

Good afternoon

I am trying to update the definition query of two layers using arcpy python 

For testing purposes, I am resetting the query, but nothing happens

from arcgis.gis import GIS
from arcgis.mapping import WebMap

gis = GIS("Pro")

webmap_item = gis.content.get("-..webmapid....")

web_map = WebMap(webmap_item)

# Get all layers from the web map

for layer in web_map.layers:
  print(layer.title)
  if layer.title == "first layer":
     layer.definitionQuery = None   
  if layer.title == "second layer":
       layer.definitionQuery = None

webmap_item.update()   ==>> It looks like this update does not work

[DavidPike]

It's been a while but I think the Webmap doesn't contain feature layers where you can update line that.  It's a big block of JSON - could be wrong however .  I'd try something like:

for layer in web_map.definition["operationalLayers"]:
    if layer["title"] in ["first layer", "second layer"]:
        if "layerDefinition" in layer:
            layer["layerDefinition"]["definitionExpression"] = "<insert definition query>"

webmap_item.update({"text": json.dumps(web_map.definition)})