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Kenil Vasani
Kenil Vasani

Kenil Vasani

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Asked: 2020-12-11T20:35:41+00:00 In:

TypeError: Object of type ‘float32’ is not JSON serializable

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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
jsonnumpypython
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    1. Rohit Patel

      Rohit Patel

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      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

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