How to parse null parameters in scripts

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1

I'm trying to write a script transform that will take the JSON below and delete any leaf nodes with {label: null}.

[
  {
    "icon": {
      "path": "XXX",
      "style": {},
      "color": ""
    },
    "expanded": true,
    "label": "XXX",
    "data": {
      "EqType": XXX,
      "EqEnabled": true,
      "EqName": "XXX",
      "EqPath": "XXX",
      "EqID": 1
    },
    "items": [
      {
        "icon": {
          "path": "XXX/XXX",
          "style": {},
          "color": ""
        },
        "expanded": true,
        "label": "XXX",
        "data": {
          "EqType": "XXX",
          "EqEnabled": true,
          "EqName": "XXX",
          "EqPath": "XXX/XXX",
          "EqID": 1
        },
        "items": [
          {
            "icon": {
              "path": "XXX/XXX",
              "style": {},
              "color": "var(--error)"
            },
            "expanded": false,
            "label": "QA Test Area",
            "data": {
              "EqType": "XXX",
              "EqEnabled": false,
              "EqName": "QA Test Area",
              "EqPath": "XXX/XXX/XXX",
              "EqID": 11
            },
            "items": [
              {
                "icon": {
                  "path": "material/block",
                  "style": {},
                  "color": "var(--error)"
                },
                "expanded": false,
                "label": null,
                "data": {
                  "EqType": "XXX",
                  "EqEnabled": null,
                  "EqName": null,
                  "EqPath": null,
                  "EqID": null
                },
                "items": []
              }
            ]
          }
        ]
      }
    ]
  }
]

However, I have not been able to figure out a way to write a Python conditional that checks if label: null. This is what I attempted to do in the if statement below:

def transform(self, value, quality, timestamp):
	for enterprise in value:
		for site in enterprise["items"]:
			for area in site["items"]:
				for line in area["items"]:
					if line["label"] == None:
						del line

If someone could tell me how to check if a perspective property is null in Python, that would be very helpful.

2

try

if line["label"] is None:

or

if not line["label"]:

1 Like
3

You should review the error(s) you are seeing closely, I am guessing you are seeing things like:

name 'null' is not defined, etc.

You are not dealing with a None, you are dealing with a variable written as "null", if you want it to be treated as None then set that variable at the start of the script:

null = None

This is also true for variables like "true" because Python's true bool is: True

4

I'm not getting any errors when I run the script. My problem is that I would like for the script to delete any nodes with label: null from the json tree, but the script is not doing so, instead returning the initial json tree with zero modifications whatsoever.

5

Did you remove the return at the end of the transform?

It is assumed the custom script will end with a Return comment that is a single output value, dataset, document, or other type of data.

6

I've ensured that there is a return statement at the end of the transform. I also cloned value into the return variable tree to ensure that the code is not returning the original value variable.

def transform(self, value, quality, timestamp):
	tree = value[:]
	
	for enterprise in tree:
		for site in enterprise["items"]:
			for area in site["items"]:
				for line in area["items"]:
					if line["label"] == None:
						del line
	
	return tree

Unfortunately. I'm still getting the same behavior. tree still contains the item

{
  "icon": {
    "path": "material/block",
    "style": {},
    "color": "var(--error)"
  },
  "expanded": false,
  "label": null,
  "data": {
    "EqType": "line",
    "EqEnabled": null,
    "EqName": null,
    "EqPath": null,
    "EqID": null
  },
  "items": []
}

with label: null that I am trying to remove from the json tree.

7

What @danieltalbot said.
JSON defines "a key with no value" with the keyword null (not in quotes).
Python defines the same concept as a singleton object automatically imported as None.
The idiomatic way to check whether something is null/not present in Python is with if x is None: or if x is not None:.

8

Like this?

def transform(self, value, quality, timestamp):
	tree = value[:]
	
	for enterprise in tree:
		for site in enterprise["items"]:
			for area in site["items"]:
				for line in area["items"]:
					label = line["label"]
					if label is None:
						del line
	
	return tree

I attempted this, but the code is acting the same as before. It is not deleting the line node with label: null from tree.

9

I'm guessing that area["items"] is an array of line objects.

Try this:

def transform(self, value, quality, timestamp):
	tree = value[:]
	
	for enterprise in tree:
		for site in enterprise["items"]:
			for area in site["items"]:
				for i, line in enumerate(area["items"]):
					label = line["label"]
					if label is None:
						del area[i]
	
	return tree
10

I attempted your code, and it seems to be attempting to perform the deletion, thankfully.

However, the script errors out because the del statement throws the error TypeError: 'com.inductiveautomation.perspective.gateway.script.DotReferenceJythonMap' object doesn't support item deletion

11

You need to make a copy of the tree, probably recursively, where you simply do not copy the items you would otherwise delete.

1 Like
12

So far, the only working solution I've managed is by converting value from a JsonifiableArrayList to a List[Dict], then using a line_index variable and the pop() method to remove the line from the area.

def transform(self, value, quality, timestamp):
	import json
	tree = value[:][0].toString()
	tree = [json.loads(tree)]
	
	for enterprise in tree:
		for site in enterprise["items"]:
			for area in site["items"]:
				line_index = 0
				for line in area["items"]:
					label = line["label"]
					if label is None:
						area["items"].pop(line_index)
					line_index += 1
	
	return tree

For some reason, the del keyword does not remove the line from the items list, but pop() does.

13 
def transform(self, value, quality, timestamp):
	for enterprise in value:
		for site in enterprise["items"]:
			for area in site["items"]:
				area['items'] = filter(lambda l: l['label'] is not None, area['items'])
				# area['items'] = [l for l in area['items'] if l['label'] is not None]
	return value

Didn't try it but I believe it should do what you want.
In comment, a comprehension version if that looks clearer to you.

2 Likes