Why is flask jsonify method slow?

Question

I am writing an API in a flask that returns json. Each bulb function has the form

from flask import jsonify @app.route('/getdata') def get_data(): data = load_data_as_dict() return jsonify(data) 

If I return a large amount of data, calling this function will take about 1.7 seconds. However, if I do this:

 from flask import Response @app.route('/getdata') def get_data(): data = load_data_as_dict() data_as_str = json.dumps(data) return Response(response=data_as_str, status=200, mimetype="application/json" 

... the function completes in about 0.5 seconds.

Can someone tell me why jsonify so much slower? Is there anything wrong with returning the original response to the flask instead?

Thanks!

Answer 1

I guess it has a lot to do with indenting and dumping pretty json. Here's the definition of the method (I split the comments to save space, the full code can be found here ):

 def jsonify(*args, **kwargs): indent = None separators = (',', ':') if current_app.config['JSONIFY_PRETTYPRINT_REGULAR'] and not request.is_xhr: indent = 2 separators = (', ', ': ') if args and kwargs: raise TypeError('jsonify() behavior undefined when passed both args and kwargs') elif len(args) == 1: # single args are passed directly to dumps() data = args[0] else: data = args or kwargs return current_app.response_class( (dumps(data, indent=indent, separators=separators), '\n'), mimetype=current_app.config['JSONIFY_MIMETYPE'] ) 

dumps wraps simplejson.dumps if the module is available, otherwise it uses json.dumps .

What performance will you get if you run your code with the same arguments?

Answer 2

The documentation says that:

This function wraps dumps () to add a few enhancements that make life easier. It turns JSON output into a Response object with application / json mimetype.

Thus, it does the same thing, you get a Reponse object in both cases , but since it is a convenient function, it probably works more than lightweight, which means extra time.

EDIT: actually looking again at the docs:

For clarity, the behavior of JSON serialization has the following differences from dumps (): The only argument: Passed directly to dumps ().

Can you check both return jsonify(data) and return json.dumps(data) ? They must match.