Json -> Exec Function for Python

General
1

I have seen many topics in here about getting a json input into an exec call for python but a lot of the posts end before the answer is ever found.

I have several python calls I intend to make in the node red dashboard, that will take in static JSON objects. To do this, I created a "TEMPLATE" node, which houses my json data.

In order to get the data prepped for the exec call, I have the TEMPLATE format set to "Plain Text", and output as "Parsed JSON". I then send this to a JSON node. Lastly, this is sent to my exec call.

I append the msg.payload to the exec call and printing it as:

import sys
print(sys.argv[1])

The issue is, sys.argv will strip the quotations off of my json object, so I cannot load it as json. I saw in another post someone mentioning using ARGPARSER instead, however, I do not know how to add an arguement using the EXEC node in node-red.

Here is an output from my python script where you can see "controls" has no quotations and so on.

{controls:{Sample1:{flowrate:10,direction:aspirate,valveposition:output}},stopcondition:User}

So my questions are:

  1. Is there a way to read in JSON in a python script from the exec node with the quotations intact without using an argparser?

  2. If "1" is not possible, how can I use argparser with the exec node. i.e. how do I add named parameters to the exec node

2
  1. Good question. There certainly ought to be.
  2. The example using argparse which someone mentioned is intended to handle arguments passed as a JSON string, so it's a fair bet that it can handle more than one data element within a JSON string.

Here is a python script try.py

import argparse
import json

# Set up the argument parser
parser = argparse.ArgumentParser()
parser.add_argument('JSON', metavar='json',type=str, help='JSON to parse')

args = parser.parse_args()

# Get JSON data
json_str = args.JSON

# Parse JSON data
json_data = json.loads(json_str)

print(json_data["name"])
print(json_data["age"])

Here is a simple flow

Untitled 4
Untitled 41217×74 10.4 KB 

[{"id":"0e8ff8e87d0fdf7d","type":"inject","z":"aefbc0d924a8ddfd","name":"Parameter JSON as string","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"{\"name\":\"Bill\", \"age\":42}","payloadType":"str","x":150,"y":60,"wires":[["4f2b8f306542ca0c"]]},{"id":"f3a0d09e7688f675","type":"exec","z":"aefbc0d924a8ddfd","command":"python /home/pi/try.py ","addpay":"payload","append":"","useSpawn":"false","timer":"","winHide":false,"oldrc":false,"name":"","x":580,"y":60,"wires":[["2a4b7edae62b0713"],["2a4b7edae62b0713"],[]]},{"id":"2a4b7edae62b0713","type":"debug","z":"aefbc0d924a8ddfd","name":"debug 294","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":770,"y":60,"wires":[]},{"id":"4f2b8f306542ca0c","type":"change","z":"aefbc0d924a8ddfd","name":"Wrap it in 'quotes'","rules":[{"t":"set","p":"payload","pt":"msg","to":"\"'\" & payload & \"'\"","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":370,"y":60,"wires":[["f3a0d09e7688f675"]]}]

It works for me (on Linux); I read the other post and did a couple of experiments.
Please see if it works for you and let us know.