Send Python information to a JavaScript file

Question

I am new to Python and JavaScript and (attempting) to use cola.js. My HTML form sends information to Python, which turns it into an array of dictionaries.

Class_Name(ndb.Model):
    class_title = ndb.JsonProperty()
def post(self):
    classname = self.request.get('classname') #user inputs 1 classname
    prereq = self.request.get('prereq') #user inputs 1 prereq
    new_dictionary = {}
    new_dictionary [classname] = prereq
    new_class = Class_Name(class_title = new_dictionary) #stores as a dictionary
    new_class.put()

    Class_data = Class_Name.query().fetch() #gets all instances of Class_Name

   *** code that goes in b/w sends back to input form if want to add more classes, else, goes to below code

        output = []
        for a in Class_data:
            jsonprop = a.class_title
            extracted_output = json.dumps(jsonprop)
            output.append(extracted_output)
        template_vars= {'Class_data': output}
        template = jinja2_environment.get_template('template/post.html')
        self.response.write(template.render(template_vars))

This is my basic code so far. I want to use cola.js to turn my information into a graph, basically mapping out each class with its prerequisites. However, the cola.js format is a JavaScript file that looks like this:

graph = {
  nodes: [
  {
    id: 'A'
  }, {
    id: 'B'
  }, {
    id: 'C'
  }
],

links: [
  {
    id: 1,
    source: 'A',
    target: 'B'
  }, {
    id: 2,
    source: 'B',
    target: 'C'
  }, {
    id: 3,
    source: 'C',
    target: 'A'
  }
]
};

Is there any way I can tell JavaScript to get my Python array, and enter the info into the JavaScript file like this?

graph = {
  nodes: [
  {
    id: 'Class1' **will put actual class name
  }, {
    id: 'Class2'
  }
],

links: [
  {
    id: 1,
    source: 'Class1',
    target: 'prereq'
  }, {
    id: 2,
    source: 'Class2',
    target: 'prereq'
  }
]
};

This is a rough code for turning my Python information into the JavaScript format.

nodes_array = []
nodes_dict = {}
links_array = []
links_dict = {}
graph_array = []

#loops through every element
for a in Class_data:
    jsonprop = a.class_title
    extracted_output = json.loads(jsonprop)

for c_class, prereq in extracted_output.iteritems():
    # for the links dictionary  
    counter_link = 1
    # creates {'id':'class1'}
    nodes_dict['id'] = c_class
    #creates [ {'id':'class1'},  {'id':'class2'}]
    nodes_array.append(nodes_dictionary)
    # creates {'id': 'counter', 'source': 'class1', 'target': 'prereq'}
    links_dictionary[id] = counter_link
    counter_link++
    links_dictionary[source] = c_class
    links_dictionary[target] = prereq
    # creates [{'id': 'counter', 'source': 'class1', 'target': 'prereq'}]
    links_array.append(links_dictionary)
    #creating the format --> 'nodes': [  {id: class1}, {id:class2},  {id:class3} ]"
    #creating the format --> 'links': [  {id: 1, source :class2, target :class3} ]"
    graph[nodes] = nodes_array
    graph[links] = links_array

Answer 1

Your Python script can use the json module to write the graph to a file in a format that JavaScript understands.

If you do this in Python:

import json

graph = {
    'nodes': [ {'id': 'Class1'}, {'id': 'Class2'} ],
    'links': [
        { 'id': 1, 'source': 'Class1', 'target': 'prereq' },
        { 'id': 2, 'source': 'Class2', 'target': 'prereq' }
    ]
}

with open('graph.js', 'w') as out_file:
  out_file.write('var graph = %s;' % json.dumps(graph))

The result is a file named graph.js, containing this:

var graph = {"links": [{"target": "prereq", "source": "Class1", "id": 1}, {"target": "prereq", "source": "Class2", "id": 2}], "nodes": [{"id": "Class1"}, {"id": "Class2"}]};

If you load graph.js before loading your own JavaScript file, you can refer to the variable graph to use your graph.