Added to_string for safety
Added to_string for safety

shahankhatch/pyethereum,pipermerriam/pyethereum,ethereum/pyethereum,shahankhatch/pyethereum,inzem77/pyethereum,harlantwood/pyethereum,karlfloersch/pyethereum,ethereum/pyethereum,ckeenan/pyethereum,karlfloersch/pyethereum,vaporry/pyethereum,pipermerriam/pyethereum,holiman/pyethereum