fix: do not use asserts as part of prog flow
fix: do not use asserts as part of prog flow

jnnk/pyethereum,ethers/pyethereum,vaporry/pyethereum,ethereum/pyethereum,pipermerriam/pyethereum,karlfloersch/pyethereum,ckeenan/pyethereum,shahankhatch/pyethereum,ddworken/pyethereum,karlfloersch/pyethereum,shahankhatch/pyethereum,ethermarket/pyethereum,inzem77/pyethereum,harlantwood/pyethereum,pipermerriam/pyethereum,holiman/pyethereum,ethereum/pyethereum