# 安裝 Py-EVM 實現以太坊虛擬機

### Mac os

1. install Python 3 with brew

brew install python3

2. install pip

pip3 install -U pip

3. install py-evm package via pip

pip3 install -U py-evm

reference: https://py-evm.readthedocs.io/en/latest/guides/quickstart.html

---

### Building an app that uses Py-EVM
在local跑自己的區塊鏈

1. clone demo-app

git clone https://github.com/ethereum/ethereum-python-project-template.git demo-app

2. change into the directory

cd demo-app

3. Add the Py-EVM library as a dependency
open setup.py file and edit the following section.

install_requires=[
    "eth-utils>=1,<2",
    "py-evm==0.5.0a0",
],

並且把檔案中的 name 改成 "demo-app".

4. to install the dependencies, run

pip install -e ".[dev]"

5. create a new directory app and create a file main.py inside. Paste in the following content.

from eth import constants
from eth.chains.mainnet import MainnetChain
from eth.db.atomic import AtomicDB

from eth_utils import to_wei, encode_hex


MOCK_ADDRESS = constants.ZERO_ADDRESS
DEFAULT_INITIAL_BALANCE = to_wei(10000, 'ether')

GENESIS_PARAMS = {
    'difficulty': constants.GENESIS_DIFFICULTY,
}

GENESIS_STATE = {
    MOCK_ADDRESS: {
        "balance": DEFAULT_INITIAL_BALANCE,
        "nonce": 0,
        "code": b'',
        "storage": {}
    }
}

chain = MainnetChain.from_genesis(AtomicDB(), GENESIS_PARAMS, GENESIS_STATE)

mock_address_balance = chain.get_vm().state.get_balance(MOCK_ADDRESS)

print("The balance of address {} is {} wei".format(
    encode_hex(MOCK_ADDRESS),
    mock_address_balance)
)

6. run the script

python3 app/main.py

#### result


---
### 客製化區塊鏈
可以更改main.py 中的 GENESIS_PARAMS 或是 GENESIS_STATE參數，例如重新定義 difficulty, balance…

GENESIS_PARAMS = { 
                 'difficulty': constants.GENESIS_DIFFICULTY,        
                 'gas_limit': 3141592, 
}

reference : https://py-evm.readthedocs.io/en/latest/cookbook/index.html

###### tags: `Solidity`