How to return json using Flask web framework

My aim is to do data summary in python using Pandas and return the summary in the form of JSON. I am using the Flask web framework to return JSON.

My code to get JSON is as follows:(excluding libraries)

data = pandas.read_csv('D:myfile.csv')
for colname, dtype in data.dtypes.to_dict().iteritems():
    if dtype == 'object':
        print colname
        count = data[colname].value_counts()
        d = dict((str(k), int(v)) for k, v in count.iteritems())
        f = dict(sorted(d.iteritems(), key=lambda item: item[1], reverse = True)[:5])    
print f
json.dumps(f)

In Flask I have to do the following things:

@app.route("/summary")
def some_fn():
    # identify filename

    # do summary on file

    # send it back as json