# TypeError: Object of type datetime is not JSON serializable

**Code:** `not JSON serializable` · **Category:** Python · **Seen on:** Python

json.dumps() met a type it doesn’t know how to encode (datetime, Decimal, set, custom objects).

## Meaning

The json module only handles dict, list, str, int, float, bool and None. Convert other types or pass a default= function.

## Common causes

- datetime/date objects
- Decimal from databases
- set instead of list
- ORM model instances

## Quick fix

1. json.dumps(data, default=str) for quick conversions
2. Convert explicitly (isoformat(), float(), list())
3. Use the framework’s serializer (DRF, pydantic model_dump_json)

## Detailed fix by platform

### Python

1. `json.dumps(payload, default=lambda o: o.isoformat() if hasattr(o, "isoformat") else str(o))`

## How to diagnose

1. **Type** — Which type is named?
2. **Field** — Where in the data?

---
Source: [WhatIsMyError](https://whatismyerror.com/errors/python/typeerror-object-not-json-serializable)