Providing an API like `get_rlp_decoder_tx_hex()` for developers using RLPList to get rid of hardcoded hex in code

viper Version: 0.0.2
pyethereum Version: 2.1.0
OS: mac os
Python Version (python --version): 3.6.0

Environment (output of pip freeze):

argh==0.26.2
asn1crypto==0.23.0
astroid==1.5.3
attrs==17.3.0
bitcoin==1.1.42
bumpversion==0.5.3
certifi==2017.4.17
cffi==1.10.0
chardet==3.0.4
click==6.7
coincurve==6.0.0
colorama==0.3.9
coverage==4.4.1
coveralls==1.1
cytoolz==0.8.2
decorator==4.1.2
docopt==0.6.2
eth-testrpc==1.3.3
ethereum==2.1.0
ethereum-abi-utils==0.4.4
ethereum-keyfile==0.3.0
ethereum-keys==0.1.0a7
ethereum-serpent==2.0.2
ethereum-tester==0.1.0b2
ethereum-utils==0.6.0
flake8==3.4.1
flaky==3.4.0
future==0.16.0
graphviz==0.8
hypothesis==3.38.0
idna==2.5
isort==4.2.15
json-rpc==1.10.8

What's your issue about?

Currently if we want to use RLPList in viper code, we have to install rlp_decoder in advance. Like this

viper_rlp_decoder_tx = rlp.decode(utils.parse_as_bin("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"), Transaction)

Once the rlp_decoder tx is updated, we have to change the hex manually, otherwise error occurs due to the fact that the address of the contract changes.

How can it be fixed?

I think it will be better if we introduce a function like get_rlp_decoder_tx_hex() in viper, which outputs the hex of the rlp_decoder transaction. The most simple one like(for simplicity, just assume it is located in the viper/utils.py, though it might not be the best location of the function)

def get_rlp_decoder_tx_hex():
    return "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"

In the code which need rlp_decoder installing:

viper_rlp_decoder_tx = rlp.decode(utils.parse_as_bin(viper.utils.get_rlp_decoder_tx_hex()), Transaction)
viper_rlp_decoder_addr = viper_rlp_decoder_tx.creates

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