5 Best Methods to Convert Python Bytes Dict to JSON

💡 Problem Formulation: Python developers often need to convert a dictionary where the keys or values are bytes objects to a JSON string. For instance, when handling the output from a database query or data serialization/deserialization tasks. The input example could be {b'key1': b'value1', b'key2': [b'list', b'with', b'bytes']}, and the desired output is a JSON string like {"key1": "value1", "key2": ["list", "with", "bytes"]}. This article outlines five reliable methods to accomplish this task in Python.

Method 1: Using json.dumps with a Custom Encoder

Creating a custom encoder that inherits from json.JSONEncoder allows specifying how bytes objects should be decoded before serialization. This method provides fine-grained control over the conversion process.

Here’s an example:

import json

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

bytes_dict = {b'key': b'value'}
json_str = json.dumps(bytes_dict, cls=BytesEncoder)
print(json_str)

Output:

{"key": "value"}

The BytesEncoder class provided here extends json.JSONEncoder and overrides the default method to check and decode bytes objects. This is then passed to json.dumps via the cls parameter, returning the desired JSON string.

Method 2: Decoding Bytes Before Serialization

This straightforward approach involves decoding all bytes objects in the dictionary before passing it to json.dumps. This method is useful when the bytes objects are straightforward to decode.

Here’s an example:

import json

bytes_dict = {b'key1': b'value1', b'key2': [b'list', b'with', b'bytes']}
decoded_dict = {k.decode('utf-8'): v.decode('utf-8') if isinstance(v, bytes) else v for k, v in bytes_dict.items()}

json_str = json.dumps(decoded_dict)
print(json_str)

Output:

{"key1": "value1", "key2": ["list", "with", "bytes"]}

In this snippet, a new dictionary decoded_dict is created with all keys and bytes values decoded to strings. This dictionary is then serialized to JSON.

Method 3: Using Recursion for Nested Structures

When dealing with nested dictionaries or lists, recursion can be used to decode bytes throughout the entire structure. This can be particularly useful for deeply nested data.

Here’s an example:

import json

def decode_bytes(value):
    if isinstance(value, bytes):
        return value.decode('utf-8')
    elif isinstance(value, dict):
        return {decode_bytes(k): decode_bytes(v) for k, v in value.items()}
    elif isinstance(value, list):
        return [decode_bytes(item) for item in value]
    return value

bytes_dict = {b'key': {b'nested': b'value'}}
json_str = json.dumps(decode_bytes(bytes_dict))
print(json_str)

Output:

{"key": {"nested": "value"}}

This recursive function decode_bytes decodes bytes, iterates through dictionaries and lists, and applies itself to each element. The result is then serialized to JSON.

Method 4: Using a Combination of ast.literal_eval and json.dumps

This method first converts bytes to strings using ast.literal_eval, which safely evaluates strings containing Python literals. The resultant dictionary with strings can be easily serialized with json.dumps.

Here’s an example:

import json
import ast

bytes_dict = "{b'key': b'value'}"
str_dict = ast.literal_eval(bytes_dict.replace(b'\\', '').decode('utf-8'))
json_str = json.dumps(str_dict)
print(json_str)

Output:

{"key": "value"}

The ast.literal_eval function safely evaluates the string, which is a representation of our dictionary containing bytes but processed as strings after the cleaning and decoding. Finally, it’s passed to json.dumps.

Bonus One-Liner Method 5: Comprehension with json.dumps

If the dictionary is simple and shallow, a one-liner using dictionary comprehension alongside json.dumps makes for quick conversion.

Here’s an example:

import json

bytes_dict = {b'key': b'value'}
json_str = json.dumps({k.decode(): v.decode() for k, v in bytes_dict.items()})
print(json_str)

Output:

{"key": "value"}

This one-liner uses dictionary comprehension to decode the keys and values of a bytes dictionary and then immediately serializes the result to JSON.

Summary/Discussion

• Method 1: Using json.dumps with a Custom Encoder. This provides flexibility and control in conversion. However, it requires additional class definition and might be overkill for simple cases.
• Method 2: Decoding Bytes Before Serialization. It’s simple and effective for flat dictionaries, but doesn’t work for nested structures without adjustments.
• Method 3: Using Recursion for Nested Structures. It covers nested structures and is robust for complex data types. It may not be as efficient for larger data sets due to the nature of recursion.
• Method 4: Using a Combination of ast.literal_eval and json.dumps. It works well for string representations of a bytes dictionary; however, using ast.literal_eval can be risky for input from untrusted sources and it’s less intuitive than direct decoding methods.
• Bonus Method 5: Comprehension with json.dumps. It’s a quick and concise one-liner suitable for small, simple dictionaries with the advantage of brevity, but less readability for those new to Python.