TypeError: Object of type 'float32' is not JSON serializable [duplicate]

Question

I'm working with numpy.float32 numbers and they don't go into JSON. What's the right approach to overcome this issue?

import numpy as np import json  a = np.float32(1) json.dumps(a)  TypeError: Object of type 'float32' is not JSON serializable 

Answer 1

It has to be a string, so you can have:

json.dumps(str(a)) 

EDIT:

JSON is a format for serialising object data. It doesn't really care or know about Python types, the json package tries to translate whatever object you pass json.dumps() into a string form via a conversion table that only supports some types (see doc below).

This is the reason why I think it's a good idea to just pass a string to avoid this issue: numpy.float32 just isn't in the table.

Because some have commented that explicitly passing a string to dumps "sounds wrong" I'll just add the doc here

json.dumps(obj, *, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, cls=None, indent=None, separators=None, default=None, sort_keys=False, **kw) Serialize obj to a JSON formatted str using this conversion table. The arguments have the same meaning as in dump().

Note Keys in key/value pairs of JSON are always of the type str. When a dictionary is converted into JSON, all the keys of the dictionary are coerced to strings. As a result of this, if a dictionary is converted into JSON and then back into a dictionary, the dictionary may not equal the original one. That is, loads(dumps(x)) != x if x has non-string keys.

taken from the official docs here: https://docs.python.org/3/library/json.html