TypeError: Object of type bytes is not JSON serializable

avatar

Borislav Hadzhiev

Last updated: Apr 20, 2022

banner

Check out my new book

TypeError: Object of type bytes is not JSON serializable #

The Python "TypeError: Object of type bytes is not JSON serializable" occurs when we try to convert a bytes object to a JSON string. To solve the error, call the decode() method on the bytes object to decode the bytes to a string before serializing to JSON.

Here is an example of how the error occurs.

main.py
import json my_bytes = 'hello world'.encode('utf-8') # ⛔️ TypeError: Object of type bytes is not JSON serializable json_str = json.dumps({'message': my_bytes})

We tried passing a bytes object to the json.dumps() method but the method doesn't handle bytes objects by default.

To solve the error, either remove the call to the encode() method or use the decode() method to decode the bytes object to a string.

main.py
import json my_bytes = 'hello world'.encode('utf-8') # ✅ decode bytes object json_str = json.dumps({'message': my_bytes.decode('utf-8')}) print(json_str) # 👉️ '{"message": "hello world"}' print(type(json_str)) # 👉️ <class 'str'>

The default JSON encoder handles str values, so we can decode the bytes object to a string before serializing to JSON.

The json.dumps method converts a Python object to a JSON formatted string.

The str.encode method returns an encoded version of the string as a bytes object. The default encoding is utf-8.

The bytes.decode method returns a string decoded from the given bytes. The default encoding is utf-8.

Alternatively, you can extend from the JSONEncoder class and handle the conversions in a default method.

main.py
import json class BytesEncoder(json.JSONEncoder): def default(self, obj): if isinstance(obj, bytes): return obj.decode('utf-8') return json.JSONEncoder.default(self, obj) my_bytes = 'hello world'.encode('utf-8') json_str = json.dumps({'message': my_bytes}, cls=BytesEncoder) print(json_str) # 👉️ '{"message": "hello world"}' print(type(json_str)) # 👉️ <class 'str'>

We extended from the JSONEncoder class.

The JSONEncoder class supports the following objects and types by default.

PythonJSON
dictobject
list, tuplearray
strstring
int, float, int and float derived Enumsnumber
Truetrue
Falsefalse
Nonenull

Notice that the JSONEncoder class doesn't support bytes to JSON conversion by default.

We can handle this by extending from the class and implementing a default() method that returns a serializable object.

main.py
import json class BytesEncoder(json.JSONEncoder): def default(self, obj): if isinstance(obj, bytes): return obj.decode('utf-8') return json.JSONEncoder.default(self, obj)

If the passed in value is a bytes object, we decode it to a str and return the result.

The isinstance function returns True if the passed in object is an instance or a subclass of the passed in class.

In all other cases, we let the base classes' default method do the serialization.

To use a custom JSONEncoder, specify it with the cls keyword argument in your call to the json.dumps() method.

main.py
import json class BytesEncoder(json.JSONEncoder): def default(self, obj): if isinstance(obj, bytes): return obj.decode('utf-8') return json.JSONEncoder.default(self, obj) my_bytes = 'hello world'.encode('utf-8') # ✅ pass the cls keyword argument json_str = json.dumps({'message': my_bytes}, cls=BytesEncoder) print(json_str) # 👉️ '{"message": "hello world"}' print(type(json_str)) # 👉️ <class 'str'>

If you don't provide the cls kwarg, the default JSONEncoder is used.

I wrote a book in which I share everything I know about how to become a better, more efficient programmer.
book cover
You can use the search field on my Home Page to filter through all of my articles.