Passing a Python list of coordinates to add as markers to web map (Flask)

Question

In my flask GIS app, I am passing my web map a list of coordinates from a route in my Python backend, which works as I expect it to. When I print the list it looks like this.

[['53.792614', '-1.789202'], ['53.792561', '-1.789223'], ['53.770554', '-1.751224'], ['53.712614', '-1.746287']] ... 

I am then trying to add this list of coordinates to the map as markers, in my JavaScript. I am following HERE maps documentation - https://developer.here.com/documentation/examples/maps-js/markers/markers-on-the-map - and trying to loop through each coordinate in my list, creating a new marker for each.

// These variables are dependant on the flask route that is completed
    var lat = {{latitude}}     // 53.483837
    var long = {{longitude}}     // -2.225899
    var chargepoints = {{chargepoints}}
    var coords = {{radius_coordinates}}

// REST OF MAP FUNCTION OMITTED DUE TO LENGTH

    // chargepoints = 2 if the chargepoints route is completed
        if (chargepoints = 2) {
    
          // ADD THE CHARGEPOINTS TO THE MAP
          for (var i=0; i<coords.length; i++) {
    
            var chargemarker = new H.map.Marker({lat:coords[i][1], lng: coords[i][0]}); Cmap.addObject(chargemarker);
    
            Cmap.addObject(chargemarker);
        }
        }

However when I do this, the map does not load, and I get the error - Uncaught SyntaxError: expected expression, got '&' - in my console, and I don't know where the problem is. When I look in the Web Inspector, the coords variable looks like this.

var coords = ['53.712614', '-1.746287'] 

Answer 1

Based on the error and debug message, your Python code is passing a string into the JavaScript / web side of things. This literal string is being escaped, and the escaped characters are being passed into the JavaScript code to put items on the map.

So, in your Python code you have: ['53.792614', '-1.789202']

What JavaScript is passing to the mapping function: ['53.712614', '-1.746287']

There are probably a few different places to fix this, but I'd suggest fixing it within Python by converting the strings to doubles. From your Python code, you could do that when you build up list to plot: float(device['ChargeDeviceLocation']['Latitude'])