如何在python列表中使用索引？

Question

I am trying to execute the code of pyethereum but when I was analyzing the code in pyethereum/Ethereum/hybrid_casper/consenus.py

I can't understand where the 'NULL_SENDER' value is defined and how this state.config['NULL_SENDER] will execute.

key, account = state.config['NULL_SENDER'], privtoaddr(state.config['NULL_SENDER'])

Answer 1

Let's look through all the code.

from ethereum import utils, transactions
from ethereum.common import update_block_env_variables
from ethereum.messages import apply_transaction
from ethereum.hybrid_casper import casper_utils
from ethereum.utils import privtoaddr

# Block initialization state transition
def initialize(state, block=None):
    config = state.config

    state.txindex = 0
    state.gas_used = 0
    state.bloom = 0
    state.receipts = []

    if block is not None:
        update_block_env_variables(state, block)

    # Initalize the next epoch in the Casper contract
    if state.block_number % state.config['EPOCH_LENGTH'] == 0 and state.block_number != 0:
        key, account = state.config['NULL_SENDER'], privtoaddr(state.config['NULL_SENDER'])
        data = casper_utils.casper_translator.encode('initialize_epoch', [state.block_number // state.config['EPOCH_LENGTH']])
        transaction = transactions.Transaction(state.get_nonce(account), 0, 3141592,
                                               state.config['CASPER_ADDRESS'], 0, data).sign(key)
        success, output = apply_transaction(state, transaction)
        assert success

    if state.is_DAO(at_fork_height=True):
        for acct in state.config['CHILD_DAO_LIST']:
            state.transfer_value(
                acct,
                state.config['DAO_WITHDRAWER'],
                state.get_balance(acct))

    if state.is_METROPOLIS(at_fork_height=True):
        state.set_code(utils.normalize_address(
            config["METROPOLIS_STATEROOT_STORE"]), config["METROPOLIS_GETTER_CODE"])
        state.set_code(utils.normalize_address(
            config["METROPOLIS_BLOCKHASH_STORE"]), config["METROPOLIS_GETTER_CODE"])

We can see that this code is most likely being imported by multiple programs, which it is! https://github.com/ethereum/pyethereum/blob/develop/ethereum/hybrid_casper/chain.py

If we see the usage of the function in chain.py, the state parameter is being fulfilled with self.state , it is self.state = self.mk_poststate_of_blockhash(self.db.get(b'head_hash')) .

This function returns a State object, made in ethereum.state , which can be turned into a dictionary. This most likely means that it is getting the value that corresponds to the key called 'NULL_SENDER'.