TypeError: Object Not JSON Serializable

Why This Happens

JSON only supports strings, numbers, booleans, null, arrays, and objects. Python types like datetime, set, bytes, Decimal must be converted.

The Problem

import json
from datetime import datetime
data = {'timestamp': datetime.now(), 'tags': {1, 2, 3}}
json.dumps(data)

The Fix

import json
from datetime import datetime

class CustomEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, datetime):
            return obj.isoformat()
        if isinstance(obj, set):
            return list(obj)
        return super().default(obj)

json.dumps(data, cls=CustomEncoder)

Step-by-Step Fix

1. 1

   Convert unsupported types

   Convert datetime to .isoformat(), sets to lists.

2. 2

   Use default=str

   Pass default=str as a quick fix.

3. 3

   Write a custom encoder

   Subclass json.JSONEncoder and override default().