Passing JSON data to javascript from python

Question

I'm trying to pass some data retrieved from a database with python to javascript.

The code below works. I can access the data in javascript but I can only pass one row at a time.

#!le/usr/bin/env python3
import sys
import re
import datetime
import sqlite3
import json
import time
SQLDB = '/home/daylene/db/PiLN.sqlite3'
db = sqlite3.connect(SQLDB) 
db.row_factory = sqlite3.Row
cursor = db.cursor()
sql = '''SELECT segment, dt, set_temp, temp, pid_output
               FROM firing WHERE run_id=? ORDER BY dt;
          '''
p = ((54),)
cursor.execute(sql, p)
columns = [column[0] for column in cursor.description]
results = []
for row in cursor.fetchall():
    results.append(dict(zip(columns,row)))
print(json.dumps(results[-1]))

And the working javascript

  <script>
        $(document).ready(function () {
            showGraph();
        });


        function showGraph()
        {
            $.ajax({
              mimeType: 'application/json; charset=iso-8859-1',
              url:  'data.cgi',
              //data: JSON.stringify( query ),
              contentType: "application/json",
              dataType: 'json',
              method: 'POST',
              async: false,
              success:  function (response)
                {
                    //document.write(response);
 
                    var time = response["dt"];
                    var temp = response["temp"];
                    //document.write(response);
                    //for (var i in response) {
                     //   time.push(response.time);
                      //  temp.push(response.temp);
                    //}

                    var chartdata = {
                        labels: time,
                        datasets: [
                            {
                                label: 'time',
                                backgroundColor: '#49e2ff',
                                borderColor: '#46d5f1',
                                hoverBackgroundColor: '#CCCCCC',
                                hoverBorderColor: '#666666',
                                data: temp
                            }
                        ]
                    };

                    var graphTarget = $("#graphCanvas");

                    var barGraph = new Chart(graphTarget, {
                        type: 'bar',
                        data: chartdata
                    });
                }
            
            
        });
    }
        </script>

uncommentating document.write(response); and changing to print(json.dumps(results)) does not work. Nothing is returned with document.write(response);

Adding this does not work

for row in results:
    results1.append(json.dumps(row))
print(results1)

and then adding this also does not work

results1 = []
for row in results:
    results1.append(json.dumps(row))
print(json.dump(results1)

The output of print(results) (shortened)

[{"segment": 4, "dt": "2020-07-09 19:58:55", "set_temp": 1145, "temp": 1145.02, "pid_output": 83.49}, {"segment": 4, "dt": "2020-07-09 19:59:24", "set_temp": 1145, "temp": 1145.15, "pid_output": 80.76}, {"segment": 4, "dt": "2020-07-09 19:59:54", "set_temp": 1145, "temp": 1145.16, "pid_output": 80.6}, {"segment": 4, "dt": "2020-07-09 20:00:24", "set_temp": 1145, "temp": 1145.15, "pid_output": 80.73}, {"segment": 4, "dt": "2020-07-09 20:00:55", "set_temp": 1145, "temp": 1145, "pid_output": 83.73}, {"segment": 4, "dt": "2020-07-09 20:01:24", "set_temp": 1145, "temp": 1145.08, "pid_output": 82.1}, {"segment": 4, "dt": "2020-07-09 20:01:54", "set_temp": 1145, "temp": 1145.13, "pid_output": 80.99}]

Any guidance is appreciated.

Answer 1

Bleh, I figured it out. It wasn't the code but rather the size of the data I was trying to pass. Trying a smaller array worked fine.

I finally thought to check the lighttpd logs and I'm getting this.

(mod_cgi.c.588) response headers too large for /app/data.cgi

Answer 2

The easiest way to serve data to your JS frontend from Python is by making a server that serves HTTP requests.

Using simple flask for example:

from flask import Flask, jsonify

app = Flask(__name__)

@app.route("/my-data")
def get_data():

    my_data = [{"segment": 4, "dt": "2020-07-09 19:58:55"}, {}]

    return jsonify(my_data)

if __name__ == "__main__":
    app.run(port=8080, host="0.0.0.0")

And then you can request the data from http://localhost:8080/my-data in your Javascript.