Transaction class instances retain old attributes

[jseagrave21]

Current behavior

This issue was first discovered by @lock9 and then further investigated by @jseagrave21 and @ixje.

Whenever an instance of a transaction is created the creator defines attributes in this manner:

def __init__(self, inputs=[], outputs=[], attributes=[], scripts=[]):

From @ixje "The problem with this is that you should not put mutable objects (e.g. a list) as the default values. because they are created only once and then reused for all instances ever created."

This caused the issue discovered by @lock9. When creating new instances of RawTransaction, the previous attributes were retained and the new ones appended until the max (16) was reached.

Expected behavior

A new transaction class should not retain old attributes.

How to reproduce

Create a new transaction and append an attribute in a loop.

Your environment

neo-python v0.8.4
Also references https://github.com/CityOfZion/neo-python/blob/9588aed21a58cf8f9e862679fd8a8cfa778fac5e/neo/Core/TX/RawTransaction.py

[lock9]

The fix provided by @ixje solves the problem (fix Transaction class constructor):

def __init__(self, inputs=None, outputs=None, attributes=None, scripts=None):
        """
        Create an instance.
        Args:
            inputs (list): of neo.Core.CoinReference.CoinReference.
            outputs (list): of neo.Core.TX.Transaction.TransactionOutput items.
            attributes (list): of neo.Core.TX.TransactionAttribute.
            scripts:
        """
        super(Transaction, self).__init__()
        self.inputs = [] if inputs is None else inputs
        self.outputs = [] if outputs is None else outputs
        self.Attributes = [] if attributes is None else attributes
        self.scripts = [] if scripts is None else scripts
        self.InventoryType = 0x01  # InventoryType TX 0x01
        self.__references = None

Thank you for the very quick fix!