Turn Python object into JSON output

Question

New to Python, trying to define a very simple class that will hold a few values, and then get it output into JSON notation.

import json

class Multiple:
    def __init__(self, basis):
            self.double = basis * 2
            self.triple = basis * 3
            self.quadruple = basis * 4


m = Multiple(100)
json.dumps(m)

I was hoping to see something like

{
  "double":"200",
  "triple":"300",
  "quadruple":"400"
}

but instead get an error: "TypeError: <main.Multiple object at 0x0149A3F0> is not JSON serializable"

cs95 · Accepted Answer · 2017-08-23T08:45:22.870

14

You can serialise the __dict__ attribute of m:

In [214]: json.dumps(m.__dict__)
Out[214]: '{"quadruple": 400, "double": 200, "triple": 300}'

You can also call vars:

In [216]: json.dumps(vars(m))
Out[216]: '{"quadruple": 400, "double": 200, "triple": 300}'

What to use and why: Use `__dict__` or `vars()`?

For more complicated classes, consider the use of jsonpickle.

jsonpickle is a Python library for serialization and deserialization of complex Python objects to and from JSON. The standard Python libraries for encoding Python into JSON, such as the stdlib’s json, simplejson, and demjson, can only handle Python primitives that have a direct JSON equivalent (e.g. dicts, lists, strings, ints, etc.). jsonpickle builds on top of these libraries and allows more complex data structures to be serialized to JSON.

Emphasis mine.

edited Aug 23 '17 at 08:45

answered Aug 23 '17 at 08:33

cs95

379,657
97
704
746

2

beat me for a second , nice answer – Netwave Aug 23 '17 at 08:34
@DanielSanchez Next time :) – cs95 Aug 23 '17 at 08:34
4

it is better to use [`vars`](https://docs.python.org/2/library/functions.html#vars) – Azat Ibrakov Aug 23 '17 at 08:34
@AzatIbrakov, did not know about `vars` and had struggle sometimes with that. It is the useful tip of the day, thanks!! – Netwave Aug 23 '17 at 08:36
@AzatIbrakov: Why is that better? – Ry- Aug 23 '17 at 08:36
@Ryan: [this answer](https://stackoverflow.com/a/21300095/5997596) – Azat Ibrakov Aug 23 '17 at 08:38
So they handle superclass attributes identically... okay. – cs95 Aug 23 '17 at 08:39
1

@AzatIbrakov: I disagree with it in the case of `__dict__` just because `vars`’s overloading is icky. – Ry- Aug 23 '17 at 08:39
@Ryan: what do you mean by that? – Azat Ibrakov Aug 23 '17 at 08:41
@AzatIbrakov: “Without an argument, `vars()` acts like `locals()`.” That’s kind of what the name suggests it does, too. `__dict__` has one meaning and is pretty standard. – Ry- Aug 23 '17 at 08:44

Turn Python object into JSON output

1 Answers1

Linked