Python Nested object are not serializable

Question

Transaction.py

from TransactionInput import TransactionInput
import unittest
from io import BytesIO
from binascii import unhexlify
import json


class Transaction:
    def __init__(self, version, inputs):
        self.version = version
        self.inputs = inputs

    @classmethod
    def parse(cls, stream):
        version = int.from_bytes(stream.read(4), byteorder='little')

        inputs_size = int.from_bytes(stream.read(1), byteorder='big')
        tx_inputs = []
        for i in range(0, inputs_size):
            tx_input = TransactionInput.parse(stream)
            tx_inputs.append(tx_input)

        return cls(version, tx_inputs)


class TestTransaction(unittest.TestCase):
    def test_parse(self):
        raw_transaction = '0100000001280594d0869749bd0f0e76074637a41a534cf96b0f7787aafe36f2c466ae3c50000000006b48304502204b39b9d63d0718052bd64c120f768a5eb083a8184a31409520104bc2a508af4f022100f62d5ce8b74a61e0075b8f3dc14df8b2e4714a962a0644e458d56bd1cb92915e012103ca545c610051cb0cca1539d95b58dd87075f97e154e9c652bafe4379424c1ba9ffffffff02672df26d010000001976a91485c359dfc971723d6724d42c60b362cce7fe01d488ac4029a1d1000000001976a9147c228e5f129213301b84b3a28aa22bf3556568e588ac00000000';
        bytes = unhexlify(raw_transaction)
        transaction = Transaction.parse(BytesIO(bytes))
        print(json.dumps(vars(transaction), sort_keys=True, indent=4))


if __name__ == '__main__':
    unittest.main()

TransactionInput.py

from ScriptSig import ScriptSig
from binascii import hexlify


class TransactionInput:
    def __init__(self, prev_tx_hash):
        self.prev_tx_hash = prev_tx_hash

    @classmethod
    def parse(cls, stream):
        prev_tx_hash = hexlify(stream.read(32)).decode('ascii')
        return cls(prev_tx_hash)

error

TypeError: Object of type 'TransactionInput' is not JSON serializable

I have Transaction object which has nested objects of type TransactionInput. i am trying to convert this transaction object into JSON. when i do this without inner object, it worked. But upon adding inner object, it raised an error. can someone help me? I am open to better solutions/libraries for JSON coversion

carrdelling · Accepted Answer · 2018-01-29 00:39:35Z

The problem is that your transaction object contains a member of type TransactionInput (which is not serializable - only basic types, lists and dictionaries are):

{'version': 1, 'inputs': [<TransactionInput.TransactionInput object at 0x1082cd0f0>]}

There are several options to fix this, but since what you are using are relatively simple objects I would suggest handling the serialization by yourself:

class TransactionInput:
    def __init__(self, prev_tx_hash):
        self.prev_tx_hash = prev_tx_hash

    def to_json(self):
        """ This serializes each TransactionInput"""
        return "{{prev_tx_hash: {}}}".format(self.prev_tx_hash) 

 class Transaction:
    def __init__(self, version, inputs):
        self.version = version
        self.inputs = inputs


    def to_json(self):
        """ This serializes the whole Transaction object"""
        inputs_json = ','.join(_input.to_json() for _input in self.inputs)

        return '{{version: {}, inputs: [{}]}}'.format(self.version, self.inputs)

With that, you can just serialize your Transaction calling transaction.to_json() and your test will pass.

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