Flask jsonify: object is not iterable

Question

I have a class looking like the following:

class Sound(SoundJsonSerializer):
    def __init__(self, name, length):
        self.name = name
        self.length = length

where SoundJsonSerializer enabling my custom JSONEncoder to serialize this object into JSON:

{
    "name": "foobar",
    "length": 23.4
}

Now I want one of my requests to respond exactly with the above JSON.

@app.route('/sounds/<soundid>')
def get_sound(soundid):
    s = Sound("foobar", 23.4)
    return jsonify(s)

yields an error claiming s was not iterable which is true. How do I make the method return my wanted JSON?

I know I can do it by explicitly creating a dict from my Sound object like this:

    return jsonify({"name": s.name, "length": s.length})

But this seems really ugly to me. What's the preferred way to achieve my goal?

Actually, I would prefer the way that you deem "ugly". If you do this often enough, then perhaps make the creation of the dictionary into a function that takes the object and a list of strings representing the attributes you want included (or perhaps excluded) and create the dictionary (using dir() and getattr()). — Mark Hildreth
– Mark Hildreth, Commented Dec 19, 2013 at 20:09
Yeah this issue is pretty annoying, so I decided to patch Flask to make it work. — Nick Retallack
– Nick Retallack, Commented Oct 20, 2014 at 8:26

Wondercricket · Accepted Answer · 2013-12-19 02:20:36Z

3

You could possibly try this work around:

class Sound():
    def __init__(self, name, length):
        self.name = name
        self.length = length

@app.route('/sounds/<soundid>')
def get_sound(soundid):
    s = Sound('foobar', 23.4)
    return jsonify(s.__dict__)

answered Dec 19, 2013 at 2:20

Wondercricket

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2 Comments

Paolo Casciello Over a year ago

This is not a good practice as it exposes all the class internals, not only the attributes he wants

Sandra Over a year ago

@PaoloCasciello is right, there might only be a subset of attributes that I want in the JSON representation. That's what my custom JSONEncoder takes care of.

CodeLikeBeaker · Accepted Answer · 2013-12-19 14:25:52Z

You can do this a couple of different ways. The safest way to ensure that you only return what you want is to do it like this:

class Sound():
    name = None
    length = None
    test = "Test"

    def __init__(self, name, length):
        self.name = name
        self.length = length

@admin_app.route('/sounds/<sound_id>')
def get_sound(sound_id):
    s = Sound('foobar', sound_id)
    return jsonify(vars(s))

By defining the name = None, length = None as part of the class level variables, you can use the vars() versus the __dict__

When you instantiate the class through the __init__, and set the variables there, the jsonify will only return what you set via the __init__.

Result with above code:

{
"length": "1",
"name": "foobar"
}

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