How to convert all Decimals in a Python data structure to string?

decimal, dictionary, flask, json, python

Solution

You can override the application's JSON encoder by setting the `json_encoder` attribute on your application instance:

import flask

app = flask.Flask(...)
app.json_encoder = MyJSONEncoder

Then you can sub-class Flask's `JSONEncoder` and override the `default()` method to provide support for additional types:

import decimal
import flask.json

class MyJSONEncoder(flask.json.JSONEncoder):

    def default(self, obj):
        if isinstance(obj, decimal.Decimal):
            # Convert decimal instances to strings.
            return str(obj)
        return super(MyJSONEncoder, self).default(obj)

Problem

I'm building a website using Flask from which I use the jsonify method a lot to convert mostly dictionaries to Json. The problem is now that I also use Decimals a lot, and unfortunately jsonify cannot handle Decimals: ``` jsonify({'a': Decimal('1')}) ``` leads to: ``` === (a long stacktrace preceding this) === File "/usr/local/lib/python2.7/dist-packages/flask/json.py", line 83, in default return _json.JSONEncoder.default(self, o) File "/usr/lib/python2.7/json/encoder.py", line 184, in default raise TypeError(repr(o) + " is not JSON serializable") TypeError: Decimal('1') is not JSON serializable ``` So I wanted to wrap jsonify in a method like this: ``` def myOwnJsonify(item): if isinstance(item, Decimal): return flask.jsonify(str(item)) else: return flask.jsonify(item) ``` unfortunately, this doesn't convert Decimals which reside within a dict or list. How can I convert all Decimal numbers within a python data structure (be it a list, a dict, a tuple, etc.) into a string so that I can safely convert the datastructure into json?

Original source