Borislav Hadzhiev
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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.
import json my_bytes = 'bobbyhadz.com'.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.
encode
to solve the errorTo solve the error, either remove the call to the encode()
method or use the
decode()
method to decode the bytes object to a string.
import json my_bytes = 'bobbyhadz.com'.encode('utf-8') # ✅ decode bytes object json_str = json.dumps({'message': my_bytes.decode('utf-8')}) print(json_str) # 👉️ '{"message": "bobbyhadz.com"}' 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
.
BytesEncoder
class to solve the errorAlternatively, you can extend from the JSONEncoder
class and handle the
conversions in a default
method.
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.
Python | JSON |
---|---|
dict | object |
list, tuple | array |
str | string |
int, float, int and float derived Enums | number |
True | true |
False | false |
None | null |
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.
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.
To use a custom JSONEncoder
, specify it with the cls
keyword argument in
your call to the json.dumps()
method.
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.
default
keyword argument to solve the errorYou can also use the default
keyword argument in the call to the
json.dumps()
method.
import json my_bytes = 'hello world'.encode('utf-8') def json_serializer(obj): if isinstance(obj, bytes): return obj.decode('utf-8') return obj json_str = json.dumps(my_bytes, default=json_serializer) print(json_str) # "hello world" print(type(json_str)) # <class 'str'>
default
keyword argument can be set to a function that gets called for objects that can't otherwise be serialized.We defined a custom json_serializer
function that checks if the supplied value
is a bytes object.
If the value is a bytes object, we use the decode()
method to convert it to a
string.
Otherwise, the value is returned as is.