Function transferFrom

wasmtest/contracts-cplus/test_oep4.py:222–262

spender spends amount of tokens on the behalf of from_acct, spender makes a transaction of amount of tokens from from_acct to to_acct :param spender: :param from_acct: :param to_acct: :param amount: :return:

(spender,from_acct,to_acct,amount)

def transferFrom(spender,from_acct,to_acct,amount):
    """
    spender spends amount of tokens on the behalf of from_acct, spender makes a transaction of amount of tokens
    from from_acct to to_acct
    :param spender:
    :param from_acct:
    :param to_acct:
    :param amount:
    :return:
    """
    if len(spender) != 20 or len(from_acct) != 20 or len(to_acct) != 20:
        raise Exception("address length error")
    if CheckWitness(spender) == False:
        return False

    fromKey = concat(BALANCE_PREFIX, from_acct)
    fromBalance = Get(ctx, fromKey)
    if amount > fromBalance or amount < 0:
        return False

    approveKey = concat(concat(APPROVE_PREFIX,from_acct),spender)
    approvedAmount = Get(ctx,approveKey)
    toKey = concat(BALANCE_PREFIX,to_acct)

    if amount > approvedAmount:
        return False
    elif amount == approvedAmount:
        Delete(ctx,approveKey)
        Put(ctx, fromKey, fromBalance - amount)
    else:
        Put(ctx,approveKey,approvedAmount - amount)
        Put(ctx, fromKey, fromBalance - amount)

    toBalance = Get(ctx, toKey)
    Put(ctx, toKey, toBalance + amount)

    # Notify(["transfer", AddressToBase58(from_acct), AddressToBase58(to_acct), amount])
    # TransferEvent(AddressToBase58(from_acct), AddressToBase58(to_acct), amount)
    TransferEvent(from_acct, to_acct, amount)

    return True


def allowance(owner,spender):